unmapped
LC002
Unmapped
High mountain area shown as unmapped in eastern central part of quadrangle
Lake Clark
LC005
Areas of apparent bedrock in lowlands as inferred from air photos.  Scoured by glaciers and may have thin surficial cover.
bu
DI005
Possible bedrock of unknown character
Areas that air photo interpretation suggest as being underlain by bedrock.  Typically are of higher elevation than surrounding glacial deposits and show hints of structure.  In one case, an apparent strike and dip of bedding is perceptible on air photos.
Unknown
Dillingham
Sedimentary
JQu
KN007
Glacial deposits and volcanic and plutonic rocks, undivided
Quaternary, Tertiary to Jurrassic
Kenai
Igneous
KN008
?
LC006
Bedrock? of unknown character
Areas on Wes Wallace field compilation that are shown with "?"
TA015
Undifferentiated bedrock
Areas of apparent bedrock or areas of known bedrock that appear different than surrounding outcrops.  In some cases, this will be areas in otherwise surficial deposits that show unusual high relief or possible bedding.  In areas of known bedrock, this ma
Taylor Mountains
TA019
Qu
DI002
Undifferentiated surficial deposits
Mainly unsorted gravel, sand, and silt produced and deposited by action of wind, water, frost, and solifluction.
Quaternary
Unconsolidated
Qs
IL002
Surficial deposits
Unsorted to well-sorted alluvial, colluvial, glacial, glaciofluvial, lacustrine, marine, and eolian deposits
Quaternary (Holocene and Pleistocene)
Iliamna
IL006
Qcaf
IL008
Colluvium, alluvium, lacustrine, and floodplain deposits
Quaternary (Holocene)
KN002
Tertiary (Eocene and Paleocene?)
KN003
none
Drift River delta
Drift river delta, no description
Mainly unsorted gravel, sand, and silt produced, deposited, and reworked by action of wind, water, glaciers, and frost, including solifluction.  In many areas of the map, this unit is a mixture of surrounding surficial deposit units that could not be rea
KN009
Quaternary surficial deposits
Undivided surficial deposits
KN011
KN012
Unconsolidated deposits
Moraine, till, glacial outwash, alluvium, and colluvium, undivided
Terminal and lateral moraines of alpine glaciers, ground moraine and bedrock cored drumlins.  Widespread outwash.
Q
Quaternary and unmapped
Undivided Quaternary deposits and unmapped areas.
LC012
Alluvial, colluvial, and glacial deposits
SV002
Seldovia
SV005
TA002
TA003
Quaternary deposits
Mainly unsorted gravel, sand, and silt produced and deposited by action of wind, water, frost, and solifluction. (Added, not in source)
TA004
TA005
TA009
Includes flood plain, glacial, silt, and gravel deposits.
TA010
TA011
TA012
Qal
TA020
Alluvial deposits
Includes alluvium and glaciofluvial deposits.  Alluvium in minor streams not shown
Qsb
Glacially scoured possible bedrock of unknown character
Scoured bedrock
Glacially scoured bedrock; may be covered with thin glacially derived deposits; air-photo interpretation.
Glacially scoured bedrock; may be covered with thin glacially derived deposits; air-photo interpretation.  Within area of scoured bedrock, appears to be different bedrock.
Areas of apparent bedrock covered by thin(?) surficial deposits.
Varies
Qv
Volcanic rocks, undivided
Lava flows and associated pyroclastic rocks associated with Iliamna Volcano
Augustine Volcanics -- Lava flows
Lava flows, chiefly hypersthene-augite andesite and minor dacite and rhyolite on Augustine Volcano.
Volcanic rocks
Lava, breccia, and associated pyroclastics.  May include Tertiary volcanic rocks
Quaternary (with mixed Tertiary?)
Volcanic rocks of Redoubt Volcano
Consists of volcanic rocks and deposits associated with Iliamna, Redoubt, and Double Glacier volcanoes.  Typically restricted to immediate vicinity of these volcanic centers, however locally, debris flows and air-fall material may be somewhat distal.  Lo
Quaternary volcanic rocks
Volcanic rocks of Iliamna and Redoubt volcanoes
Andesitic lava and tuff of Iliamna Volcano
Light gray andesitic lava and yellowish-gray, opalized tuff.
Qil
IL007
Iliamna Lava flows
Light-gray hypersthene-augite andesitic lava, breccia, and associated pyroclastic debris
Qtv
Lava flows, North and South Twin volcanic center
Lava flows from the North and South Twin volcanic center.  Probably andesitic
KN005
Hv
Holocene volcanic rocks
Holocene volcanic rocks, primarily associated with Redoubt Volcano
LC007
Light-gray hypersthene-augite andesitic lava, breccia, and associated pyroclastic debris.
Qiv
LC010
Lava flows
Lava flows from the present Iliamna volcanic center.  Probably andesitic
SV004
Qap
Augustine Volcanics -- Pumice and scoria
Pumice and scoria on Augustine Volcano.
Qpd
Qjgdt
Johnson Glacier dome tephra deposits
Dome tephra
Qca
Ash-rich colluvium
Consists of tephra-rich colluvium in the vicinity of and west of Redoubt volcano.  Similar to other volcanoes, these deposits probably consist of ash and larger-sized pyroclasts.  On the flank of Redoubt Volcano, these deposits mantle and are incorporate
Qls
KN006
Deposits of Mass Wasting -- landslide deposits
Deposits of landslides, including falls, slumps, slides, and failures by lateral spreading.  Assigned NSA = 312 in vicinity of Polly Creek where this unit consists of debris flows from Mount Redoubt.
Qm
Debris flow deposits
Debris flow deposits of Crescent River valley.  Includes several small (older?) deposits in the upper valley and the 3,500-year-old debris flow in the lower valley
Qdfn
Debris flow deposits, younger Redoubt flows
Debris flow deposits on the north flank of Redoubt Volcano in the Drift River valley
Qdf2
Debris flow deposits, older Redoubt flows
Debris flow deposits of North Fork, Crescent River.  Deposits of multiple debris flows off the west and southwest flanks Redoubt Volcano.  Oldest(?) deposit is derived from west flank of Redoubt.  Next oldest deposit appears derived from presently glacia
Radiocarbon date of about 3,500 yrs. BP on youngest and most extensive debris flow.
Qdf1
Debris flow deposits of North Fork, Crescent River.  Deposits of the youngest, most extensive, and probably most fluid debris flow derived from southwest flank of Redoubt Volcano.  Flow was apparently derived from a presently glacier free valley draining
Ql
Lahar deposits
Qdf
Apparent debris flow deposits of upper Cresecent River valley.  Unusual deposits emanating from valley on east side of Crescent River valley.  Source valley is along extension of normal fault trending to the northeast and having apparent Holocene motion.
Qar
Augustine Volcanics -- Volcanic rubble and mudflows
Volcanic rubble and mudflows on Augustrine Volcano.
Qmf
Areas in Drift River valley subjected to flood scour or deposition by 1966 floods
pattern
Areas on Drift River delta subjected to flood scour or deposition prior to 1966
Areas on Drift River delta subjected to flood scour or deposition in the several decades before 1966
Qdr
Drift River delta mudflow deposits, undifferentiated
Areas of mudflow deposits, not easily separatable into the Younger and Older events
Qdr2
Older Drift River delta mudflow deposits
Areas of mudflow deposits, tending to be more heavily vegetated and tending to control location of Drift River channels
Qdr1
Younger Drift River delta mudflow deposits prior to 1957
Areas of mudflow deposits, tending to be minimally vegetated and relatively close to channel of Drift River
Qda
Debris-avalanche deposits
Volcanic avalanche deposits consisting of poorly sorted mixture of angular sand, cobbles, and boulders.  All deposits contain clasts of grey andesitic lava and yellow-orange hydrothermally altered rocks.  Estimated age is less than 1,000 years and some m
Qav
Volcanic avalanche deposits
Volcanic avalanche deposits consisting of poorly sorted mixture of angular sand, cobbles, and boulders.  All deposits contain clasts of gray andesitic lava and yellow-orange hydrothermally altered rocks.  Estimated age is less than 1,000 years and some m
Qva
Composite dome complex consisting of medium- to coarsely porphyritic hornblende andesite and dacite.
Quaternary (Pleistocene)
Three K-Ar whole-rock ages, two considered minimum ages at 627 and 763 ka and one of 887 ka.
Qjgd
Johnson Glacier dome complex
Dome complex
QTv
Scoriaceous olivine basalt on Seven Sisters and possibly andesite at West Glacier Creek
Quaterary or Tertiary (Pleistocene or Pliocene)
QTi
Basaltic andesite porphyry dikes and sills
Quaternary and Tertiary
Ts
Sedimentary rocks, undivbided
Mainly light- to medium-gray and light-tan, fine- to medium-grained tuffaceous feldspathic to arkosic wacke and siltstone containing scattered pebbles and lenticular beds of pebble conglomerate.  Micaceous clay and silt having moderately abundant glass s
Tertiary (Pliocene or Miocene)
Plant debris and carbonaceous material common but largely unidentifiable or nondiagnostic.  Picea sp. indicating a possibly middle or late Tertiary age.
Tks
Sterling Formation
Sandstone, siltstone, and some coal
Tertiary (Pliocene and Miocene)
Tsf
Interbedded, weakly lithified sandstone, siltstone, mudstone, carbonaceous shale, lignite coal, and minor volcanic ash.
Tb
Beluga Formation
Interbedded, weakly lithified sandstone, siltstone, mudstone, carbonaceous shale, coal, and minor volcanic ash.
Tertiary (Miocene)
Tkb
Tt
Tyonek Formation
Conglomerate and subordinate sandstone, siltstone, and coal
Tertiary (Miocene and Oligocene)
Tty
Tkth
Tyonek Formation and Hemlock Conglomerate (undivided)
Sandstone, conglomerate, and siltstone
Ttyh
Tclu
Copper Lake Formation -- Upper conglomerate member
Red-weathering pebble-cobble conglomerate consisting mainly of volcanic rock clasts and containing minor tuff.  Unit may be agglomerate rather than conglomerate; ranges from 50 to 100 percent fresh-appearing volcanic rock.  Quartzite, schist, greenstone,
Sandy interbeds in lower part of unit contain leaves referred to Acer disputabilis Hollick of Eocene (prabable early Eocene) age
Tcl
Tcls
Copper Lake Formation -- Sandstone and siltstone member
Sandy facies is chiefly fine- to medium-grained medium- to greenish-gray, lithic graywacke containing locally abundant tuffaceous and carbonaceous material.  Fragments include abundant quartz, schist, volcanic, and granitic rock fragments.  Interbedded s
Tcll
Copper Lake Formation -- Lower conglomerate member
Red-weathering pebble-cobble conglmerate consisting mainly of volcanic rock clasts and containing minor tuff.  Volcanic clasts constitute about 25 percent and appear to be derived for the Talkeetna Formation and not fresher-appearing Tertiary volcanic un
Twf?
West Foreland Formation
Conglomerate, sandstone, and siltstone; mostly tuffaceous, inferred from air photos, covered by thin glacial deposits
Twf
Conglomerate, sandstone, and siltstone; mostly tuffaceous
bT
Tertiary bedrock
Kenai Group and West Foreland Formation; nonmarine sandstone, siltstone, shale, and claystone and local coal
Tertiary
Tk
bT?
Poorly sorted polymictic conglomerate, graywacke, and siltstone; having interbedded tuff and local subaerial basalt flows.
Tertiary (Eocene)
Kenai Formation
Tan to light-yellow-brown conglomerate, sandstone, and laminated siltstone; few thin coal beds
Tertiary, Miocene and Oligocene?
Tv
Volcanic(?) rocks
Volcanic rocks based on photo correlation with areas of known volcanic rocks.
Tertiary?
Tvu
Tf
Andesitic to basaltic lavas and associated pyroclastic rocks.
Tertiary, middle to late?
ALT
Tda
Altered diabase(?)
Includes slightly altered to completely altered diabase and biotite basalt
Rhyolitic breccia, ash-flow tuff, flows, and intrusive rocks and subordinate mafic and intermediate flows.  Unit is thought to encompass entire Tertiary and may include Jurassic rocks of the Talkeetna Formation
K-Ar ages of 56.2 to 62.7 Ma, however unit is thought to encompass entire Tertiary and may include Jurassic rocks of the Talkeetna Formation.
Trs
Tvf
Mafic to intermediate flows
Mafic to intermediate flows of unit Tv where they constitute separate mappable entities.  Unit split into flows likely to be part of the Meshik Arc and assigned an NSACLASS of 1082 and the less certain age unit which are assigned NSACLASS of 1003
Ta
Mafic to intermediate flows of unit Tv where they constitute separate mappable entities.Unit split into flows likely to be part of the Meshik Arc and assigned an NSACLASS of 1082 and the less certain age unit which are assigned NSACLASS of 1003
Td
Intermediate, felsic and mafic dikes
Dikes of dacite, rhyolite, andesite, and rare basalt; stored in coverage as arcs, arc-code = 50, arc-para1 = 0
early Tertiary
Ar-AR isochron(?) age on andesite(?) of 57.0 Ma
Thf
Felsic porphyry
Tdi
P
Volcanic necks, sills, and dikes
Spires of basalt and diabase representing the solidified core or vent of Tertiary volcanoes.  (NOTE, this is not a map unit. but is shown using a special symbol on the map)
Thm
Tib
Intricate Basalt
Glassy to porphyritic black to dark-green olivine-augite basalt, largely in the vicinity of Intricate Bay, but also occurs south of Gibraltar Lake
Tertiary (Pliocene)
Tw
Basalt
Basalt and locally diabasic intrusive rocks
late Tertiary
K-Ar ages of 4.62 and 4.72 Ma
QTb
v
Extrusive igneous rocks
Olivine basalt flows
Tglu
Gibraltar Lake Tuff -- Upper member
Light-gray to white crystal ash-flow tuff.  Maximum thickness of 152 to 182 m
Tertiary (Pliocene?)
Tpgu
Tgll
Gibraltar Lake Tuff -- Lower member
Light- to medium-gray and tan rhyolitic crystal and lithic welded tuff and local interbedded porphyritic rhyolite flows
Tertiary (Pliocene? to Oligocene?)
Tpgl
Tvt
Volcanic rocks, undivided, tuff
Gray and purple bedded lithic, crystal, and vitric tuff; light-gray to purple welded crystal and lithic tuff most common.  Sample collected along Alagnak River by Janet Curran, USGS-WRD
Tertiary (Oligocene and older?)
40Ar/39Ar age on plagioclase of 41.6 Ma
Tvr
Tft
Felsic volcanic rocks, tuff(?)
Cream to light-gray to green layered volcanic rocks.  Layering suggests rocks are tuffaceous.
Gray, green, and purple bedded lithic, crystal, and vitric tuff; light-gray to tan welded crystal and lithic tuff most common.
Rhyolitic breccia, ash-flow tuff, and flows. Cream, light-gray, green, and purple bedded lithic, crystal, and vitric tuff; light-gray to tan welded crystal and lithic tuff most common
K-Ar ages of 41.6 ro 45.1 Ma, in adjacent quadrangles
Tvba
Volcanic rocks, undivided, basalt and andesite
Dark-gray to green glassy to porphyritic basaltic andesite and andesite lava flows.  Locally, basalt, dacite, and rhyolite are common.  Many of the rocks are associated with eruptive centers.  Unit inferred from adjacent Iliamna quadrangle geologic map.
Tm
Includes basalt, andesite, tuff, volcanic rubble, and breccia
Undifferentiated volcanic mafic and felsic flows, tuff flow breccias.  Interpreted from air photos
Rhyolitic breccia, ash-flow tuff, flows, and intrusive rocks and subordinate mafic and intermediate flows.  Unit is thought to encompass entire Tertiary and may include Jurassic rocks of the Talkeetna Fm.  Interpreted from airphotos
K-Ar ages of 56.2 to 62.7 Ma, however unit is thought to encompass entire Tertiary and may include Jurassic rocks of the Talkeetna Fm.
Dark-gray to green glassy to porphyritic basaltic andesite and andesite lava flows.  Locally, basalt, dacite, and rhyolite are common.  Many of the rocks are associated with eruptive centers.
Mafic to intermediate flows of unit Tv where they constitute separate mappable entities.  Unit split into flows likely to be part of the Meshik Arc and assigned an NSACLASS of 1082 and the less certain age unit which are assigned NSACLASS of 1003.  Infer
Andesite plug
Small andesite plug intruding hornfelsed siltstone.  Contact metamorphism is not associated with andesite plug.  Also includes isolated andesite plug in southeast corner of D-1 quadrangle.
Volcanic rocks, undivided, volcanic rubble and breccia
Volcanic rubble and breccia, including some agglomerate; may include deposits of lahars.
Tbb
Olivine basalt
Massive columnar jointed olivine basalt flows in the area east of the Stuyahok Hills; part of bimodal volcanic suite.  The sequence consists of interlayered basalt flows and felsic tuff.  Flows range from 3 to 10 m thick. SiO2 content is approximately 48
Ar-Ar age of 44 Ma
Tbep
Tbr
Bimodal volcanic suite, rhyolitic and dacitic tuff
Distinctive light colored horizons of felsic tuff interlayered with olivine basalt in the Stuyahok Hills.  Tuff composed largely of altered glass and very fresh phenocrysts of plagioclase.  Tuff layers approximately 10 to 30 m thick.  Age is approximatel
Tbo
Massive columnar jointed olivine basalt flows in the southwestern D-1 quadrangle (T.4 S., R.41 W.); overlies alaskite (unit TKga) and graywacke of probable Jurassic age (unit Jkw).  Newly determined Ar-Ar isochron age is 53.70 +/- 0.62 Ma.  SiO2 content
Tertiary (early Eocene)
Ar-Ar age of 53.70 +/- 0.62 Ma
Tvi
Ignimbrite
Crystal tuff containing variable amounts of biotite and feldspar crystals in a tuffaceous matrix.  Unit is widespread in the Stuyahok Hills and varies in appearance from crystal tuff to porphyritic plutonic rock.  However in all cases, the groundmass is
Tertiary (Paleocene)
Wallace and others (1989, DI006) report K-Ar age of 57.9 Ho, and 58.6 Bi; new Ar-Ar ages tightly cluster at 59 Ma
Tvig
Ti
Intrusive rocks
Dikes, sills, and stock-lke masses of felsic to mafic composition
Tiu
Tg
Granitic rocks
Ti13
Tertiary intrusive rocks -- Unit 13 Granite
Multiphase, hypabyssal leucocratic grayish-pink biotite granite
Ti18
Tertiary intrusive rocks -- Unit 18 Granite
Small area of fractured biotite granite containing as much as 40 percent potassium-feldspar.
Togr
Ti19
Tertiary intrusive rocks -- Unit 19 Aplite
Light-gray, fine-grained xenomorphic granular aplite stock.  Younger than Ti -- unit 17.
Fine- to medium-grained granodiorite and quartz diorite, includes volcanic necks, sills, and dikes.
Tgd
Tqd
Quartz Diorite
Coarse-grained, light-gray hornblende-biotite quartz diorite.
Tertiary (Oligocene)
36 Ma
Toqd
Ti6
Tertiary intrusive rocks -- Unit 6 Quartz monzodiorite
Small irregular body of quartz monzodiorite cutting metamorphic rocks and containing abundant mafic inclusions.
Toem
Ti14
Tertiary intrusive rocks -- Unit 14 Quartz monzodiorite
Heterogeneous, intensely sheared and locally altered medium- to fine-grained rocks ranging from tonalite to monzodiorite.  Intruded by Ti unit 13 and intrudes Mesozoic metavolcanic rocks.
Taqd
Ti15
Tertiary intrusive rocks -- Unit 15 Tonalite
Compositionally variable medium-grained, slightly foliated tonalite and quartz diorite
K-Ar ages between 31 to 35 Ma
Ti16
Tertiary intrusive rocks -- Unit 16 Granodiorite
Medium-gray, medium-grained hypidiomorphic-granular biotite-hornblende granodiorite.  According to Reed and Lanphere, is part of Merrill Pass sequenceBiotite granite and biotite-hornblende granite and granodiorite.  Possibly two population, uniformly gra
Ti4
Tertiary intrusive rocks -- Unit 4 Granodiorite
Medium- to coarse-grained biotite-hornblende granodiorite.
Tegr
Ti12
Tertiary intrusive rocks -- Unit 12 Granite and granodiorite
North of Currant Creek, consist of grayish-white coarse-grained biotite granite; south of Currant Creek consist of medium- to coarse-grained granodiorite.
Ti17
Tertiary intrusive rocks -- Unit 17 Granite
Biotite granite and biotite-hornblende granite and granodiorite.  Possibly two populations, uniformly grayish-white, coarse-grained biotite granite containing light-pink perthite phenocrysts north of Township 9 N.  In T. 9 N and southward, rocks are less
K-Ar ages between 35 and 41 Ma
Granodiorite
Medium- and coarse-grained biotite granodiorite
U-Pb monazite age of 56.0, Ar-Ar biotite ages of 54.2, 53.2, 53.4,53.7, and 54.0
Ti5
Tertiary intrusive rocks -- Unit 5 Gabbronorite
Small, coarse-grained stock of hornblende and biotite-bearing olivine gabbronorite cutting Mesozoic sedimentary rocks.
Tgl
Ti10
Tertiary intrusive rocks -- Unit 10 Granite
Medium-grained composite pluton of granite and granodiorite which forms western border of Alaska-Aleutian Range batholith from Little Lake Clark southwestward into the Ilianma quadrangle.
Tpgr
Ti7
Tertiary intrusive rocks -- Unit 7 Granite
Coarse- to medium-grained granite.
Thgd
Ti11
Tertiary intrusive rocks -- Unit 11 Granodiorite
Medium-grained composite body largely of granodiorite but including granite and quartz monzodiorite.  Locally includes rocks of Ti10.
Ti3
Tertiary intrusive rocks -- Unit 3 Peralkaline granite
Mostly medium-grained hypidiomorphic granular granite containing subhedral to euhedral perthite.  Only peralkaline granite associated with Alaska-Aleutian Range bathoilth and probably not related to calc-alkaline rocks of the batholith.
Ti9
Tertiary intrusive rocks -- Unit 9 Granodiorite
Medium-grained, equigranular hornblende-biotite granodiorite.  Intrudes Jurassic unit 2.
Ti1
Tertiary intrusive rocks -- Unit 1 Granodiorite
Compositionally variable, medium-grained hypidiomorphic granular igneous rock, which depending on perthite content ranges from granodiorite to tonalite.
Concordant K-Ar age of  61 Ma
Ti2
Tertiary intrusive rocks -- Unit 2 Quartz monzodiorite
Medium- to fine-grained hypidiomorphic granular hornblende-biotite quartz monzodiorite.  Cut by Ti unit 10.
Ti8
Tertiary intrusive rocks -- Unit 8 Granodiorite
Largely medium-grained, equigranular hornblende-biotite silicic granodiorite but ranges from granite to quartz monzodiorite.  Intrudes Jurassic and Cretaceous rocks of Alaska-Aleutian Range batholith.
TKv
Tertiary and (or) Cretaceous
TKv?
TKp
Tuff, tuff breccia, and breccia
Compositionally undetermined tuff, tuff breccia, and breccia
Tertiary (Paleocene) or Late Cretaceous
Felsic hypabyssal rocks
The larger of scattered occurrences of felsic hypabyssal rocks.  Occurs as dikes and small plugs.
TKi7
Tertiary and (or) Cretaceous intrusive rocks -- Unit 7 Rhyolite dikes
Rhyolite dikes containing phenocrysts of sanidine and high temperature quartz.
TKgp
TKr
Hypabyssal intrusive igneous rocks
Dikes, sills, and small plugs are primarily porphyritic rhyolite.
TKg
Rhyolite flows and tuff
Rhyolite flows and tuff, includes some dikes.  Inferred on basis of Eakins and others (1978).
Rhyolite flows and tuff, includes some dikes
Tertiary or Cretaceous
ALT-SER
TKd
Dacite flows and pyroclastic rocks
Dacite flows and pyroclastic rocks, includes some hypabyssal intrusions.  Added from air-photos
Dacite flows and pyroclastic rocks, includes some hypabyssal intrusions
TKb
Basalt flows
Basalt flows.  Added from air-photos
TKu
Plutonic rocks, undivided
Plutonic rocks
Tertiary and Cretaceous
LC011
DI003
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink, plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.
K/Ar age range of 62.5 to 72.5 m.y. from biotite and hornblende
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.  In general, alkali content of these rocks is high relative to normal for their SiO2 content (LeMai
K-Ar and 40Ar-39Ar ages range from 61 to 67 Ma from biotite and hornblende
HFS
TKgm
DI009
Granitic rocks and mixed hornfels and dikes
Fine-, medium-, and coarse-grained, light- to dark-gray, plutonic granitic rocks mixed with felsic dikes and contact metamorphosed volcanic or sedimentary rocks.  Outcrop area is south of the Northern pluton, at much lower elevation, suggesting that it m
65.26 +/- 0.06 Ma on biotite
Granitic rocks of Tertiary and (or) Cretaceous age
TKg?
TA006
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.
Granitic rocks.
Intrusive igneous rocks
Primarily granite but ranges in composition from diorite to granite.  Dikes sills, and small plugs are primarily porphyritic rhyolite.
Granitic rocks, Kemuk pluton
Coarse-grained pyroxene alkali-feldspare granite.  Consists primarily of perthitic feldspar grains surrounded by a fine-grained matric of quartz and feldspar.  Contains biotite, pyroxene, and amphibole.
40Ar-39Ar age of 64.45+/- 0.11
The Akuluktuk and Tikchik Lake plutons of Wilson and others, 1977.  Medium- to Coarse-grained granite, biotite dominant but containing minor amphibole or clinopyroxene.
K-Ar and 40Ar-39Ar ages range from 69.7 to 63.4 Ma on biotite and hornblende
TKgs
Granitic rocks of the eastern Stuyahok Hills
Largely medium- to coarse-grained, light-gray to pinkish biotite monzogranite.  Large pluton widely exposed in the eastern part of the Stuyahok Hills.  Typically contains large (2cm) phenocrysts of potassium feldspar (orthoclase).  Biotite is dominant ma
K-Ar ages reported by Wallace and others (1989) are 61.2 +/- 1.8 Ma (biotite) and 54.5 +/- 1.6 Ma (hornblende, minimum age).  Ten newly determined 40Ar-39Ar ages on biotite are tightly grouped between 60.90 +/- 0.04 and 61.70 +/- 0.06 Ma and an 40Ar-39Ar
TKga
Alaskite
Coarse- to fine-grained white to off-white alaskite (alkali-feldspar granite) consisting of white feldspar and smoky quartz.  Mafic minerals and mica exceedingly sparse in this large (7 km in diameter) body on the southwestern edge of the D-1 quadrangle.
An Ar-Ar age determination on biotite yielded 66.64 +/- 0.08 Ma whereas a plateau age of potassium feldspar was 58.2 +/- 0.2 Ma, slightly older that the overlying olivine basalt (unit Tbo, 53.7 Ma) suggesting extended cooling or resetting associated with
TKi10
Tertiary and (or) Cretaceous intrusive rocks -- Unit 10 Granite prophyry
Hypidiomorphic-granular granite prophyry having quartz, plagioclase and potassium feldspar phenocrysts to 4 mm in a groundmass of 1 mm plagioclase.  Very little biotite, local muscovite and zircon.
TKi11
Tertiary and (or) Cretaceous intrusive rocks -- Unit 11 Granite
Medium-grained, xenomorphic granite, subequal biotite and hornblende.
Granite of Taylor Mountain batholith
Granite, porphyritic granite, and dikes and sills of rhyolite.
i
Primarily quartz monzonite stock but ranges in composition from grandiorite to granite.  Dikes sills, and small plugs are primarily porphyritic rhyolite.
TA014
Granite
Coarse- to fine-grained grantic rocks consisiting in part of quartz monzonite and syenite.
Granitic rocks, Kulik Lake pluton
Medium-grained pyroxene monzonite.  Contains biotite and pyroxene
TKgn
Northern pluton
Medium-grained biotite monzogranite to syenogranite found in the mountains immediately south of the Koktuli River.  Biotite is the only mafic mineral and orthoclase has moderate development of string perthite.  SiO2 of analyzed samples has a narrow range
Ar-Ar ages range between 65.50 +/- 0.05 and 66.24 +/- 0.08 Ma on biotite.
Syenitic rocks
Quartz monzodiorite of the Muklung Hills
Quartz monzodiorite but also includes granite in this large multi-phase pluton.  Large zoned, twinned and untwin feldspar phenocrysts in a fine-grained matrix of quartz, feldspar, biotite, and hornblende.
40Ar-39Ar ages range from 65.81 to 67.94 Ma from biotite
TKpsw
Pike Creek plutons, southwestern unit
Medium- to coarse-grained, light-gray biotite monzogranite or quartz monzodiorite.  Equigranular and contains more pyroxene than unit TKpnw above.  Clinopyroxene, some of which containing pinkish orthopyroxene cores is common in some samples, whereas oth
Ar-Ar biotite ages are 61.11 +/- 0.07 and 61.67 +/- 0.05 Ma
TKpe
Pike Creek plutons, eastern unit
Medium-grained, light-gray biotite monzogranite to quartz monzonite.  Hornblende to biotite ratio approximately 6:4; may contain orthoclase phenocrysts and hornblende may have relict clinopyroxene cores.  Major element chemical analysis indicates 63.2 pe
Ar-Ar age of 63.09 +/- 0.05 Ma on biotite
TKgnw
Northwest pluton
Porphyritic amphibole-bearing monzonite.  Outcrops on isolated low-relief ridge south of the Koktuli River and west of the Northern pluton.  Consists of plagioclase, amphibole (kaersutite?) , and clinopyroxene phenocrysts in a fine-grained groundmass.  S
Ar-Ar plateau age was 63.76 +/- 0.27 Ma on amphibole
TKpnw
Pike Creek plutons, northwestern unit
Medium-grained, light-gray hornblende-biotite monzogranite to quartz monzodiorite.  May contain large phenocrysts of orthoclase; biotite to hornblende ratio approximately 2:1. Two major element chemical analyses have 67.8 and 68.2 percent SiO2.
Ar-Ar biotite ages are 65.72 +/- 0.04 and 66.49 +/- 0.07 Ma
TKge
Eastern granitic rocks-Hornblende quartz monzonite
Hornblende quartz monzonite.  Texturally similar to the granitic rocks of the eastern Stuyahok Hills in having large (2 cm) feldspar phenocrysts, however hornblende is the more common mafic mineral in these rocks.  An 40Ar-39Ar age of 61.3 +/- 0.2 Ma on
Tertiary and or Cretaceous
40Ar-39Ar age of 61.3 +/- 0.2 Ma on hornblende
TKi5
Tertiary and (or) Cretaceous intrusive rocks -- Unit 5 Quartz monzonite
Numerous small intrusive bodies of quartz monzonite in the central part of the quadrangle indentified by Eakins and others (1978)
K-Ar age of 71.3 Ma on one body located in T.5N, R.30W.
TKqm
Quartz monzonite
Quartz monzonite and minor granodiorite
Tqm
Quartz monzonite.
K-Ar age of 67.1 Ma on amphibole
Primarily quartz monzonite stock but ranges in composition from granodiorite to granite.  Dikes sills, and small plugs are primarily porphyritic rhyolite.
TKi
Chiefly medium- to coarse-grained, light-gray granodiorite, quartz monzonite, and quartz diorite plutons.
TKgd
TKi13
Tertiary and (or) Cretaceous intrusive rocks -- Unit 13 Granodioritic rocks
Light-colored intrusive rocks, presumed granodiorite.
Granodiorite, quartz diorite, and diorite
Tertiary or Late Cretaceous
TKm
TKi2
Tertiary and (or) Cretaceous intrusive rocks -- Unit 2 Granodiorite
Medium- to locally fine-grained hypidiomorphic-granular, pinkish-gray granodiorite.
TKi4
Tertiary and (or) Cretaceous intrusive rocks -- Unit 4 Granodiorite
Medium- to fine-grained, light-pinkish-gray hornblende-biotite granodiorite.
TKi9
Tertiary and (or) Cretaceous intrusive rocks -- Unit 9 Granodiorite
Coarse- to fine-grained, hypidiomorphic-seriate textured granodiorite.
TKi12
Tertiary and (or) Cretaceous intrusive rocks -- Unit 12 Granodioritic rocks
TKi14
Tertiary and (or) Cretaceous intrusive rocks -- Unit 14 Granodiorite
Medium-grained, hypidiomorphic granular, seriate granodiorite  Biotite more abundant that hornblende.
K-Ar age of  64 Ma
Coarse- to fine-grained, hypidiomorphic-seriate textured granodiorite..  added from airphotos
Light-colored intrusive rocks, presumed granodiorite.  Added from air photos
Granodiorite or tonalite based on analysis and thin-sections (54AHr 10)
Granodiorite or tonalite
TKpd
Dioritic rocks
Monzodioritic rocks of Pike Creek-Largely medium-grained quartz monzodioritic and dioritic rocks in the southeast D-1 quadrangle.  SiO2 content ranges between 57.4 and 61.4 percent; as with other rocks in this region, alkalis tend to be higher that norma
Ar-Ar age of 64.42 +/- 0.04 Ma on biotite and on hornblende of 61.1 +/- 0.7 Ma which is essentially the same as the surrounding granodiorite.  As the surrounding granodiorite shows no evidence of contact metamorphism, this hornblende age should be consid
TKqd
Monzontic rocks
Coarse- to fine-grained monzogranitic to monzodioritic rocks in the southeast D-1 quadrangle.  Rocks are typically dark green, have sparse clinopyroxene, and locally show evidence of contact metamorphism.  Amphibole dominant mafic, tends to be green pleo
An Ar-Ar age of 61.3 +/- 0.2 Ma on hornblende is coeval with some parts of the Pike Creek pluton; however, as for the hornblende date on the dioritic rocks of Pike Creek (unit TKpd above), this age may represent a minimum age
TKi1
Tertiary and (or) Cretaceous intrusive rocks -- Unit 1 Diorite
Altered pyroxene gabbro and hornblende-pyroxene diorite.  Assigned Tertiary or Cretaceous age, however, Jurassic age can not be ruled out.
TKi3
Tertiary and (or) Cretaceous intrusive rocks -- Unit 3 Quartz diorite
Predominantly fine- to medium-grained altered hornblende-biotite quartz diorite and less commonly granodiorite.
TKi6
Tertiary and (or) Cretaceous intrusive rocks -- Unit 6 Diorite
Numerous small diorite intrusions in central part of quadrangle.
K-Ar age of 69.4 Ma
TKi8
Tertiary and (or) Cretaceous intrusive rocks -- Unit 8 Monzodiorite
Medium-grained, hypidiomorphic-seriate textured monzodiorite., contains subequal hornblende and clinopyroxene.
Diorite
Diorite reported northeast of Cinnabar Creek
Kk
Kaguyak Formation
Silty, thin-bedded to massive, fine- to medium-grained, green to gray arkosic wacke sandstone and interbedded siltstone.
Late Cretaceous (Campanian, Maestrichtian)
Ammonits and pelecypods, mainly Diplomoceras notabile Whiteves, Pachydiscus (Neodesmocers) sp., and Inoceramus
Kkg
Kaguyak Formation, nonmarine sedimentary rocks
Sandstone, conglomerate, siltstone and interbedded coal
Late Cretaceous
Sporomorphs:  Cranwellia striata Srivastava, Balmeisporites spp., Wodehouseia spinata Staley, Proteacidites spp., Aquilapollenites bertillonites Funjhouser, A. reticulatus Mtchediishvilli, A delicatus Stanley
Khc
Kuskokwim Group?
Photogeologic interpretation based on adjoining Taylor Mountains mapping.  Unit consists of dark siltstone and sandstone.
Cretaceous
Kuskokwim Group
Well-bedded, rhythmically interbedded dark siltstone and sandstone.  Found only north of the Koktuli River
KJs
Sedimentary rocks
Interbedded medium-gray, medium- to fine-grained lithic graywacke, silty sandstone, black shale, and local conglomerate.  Regional strike is a consistent N50E and parallel to fold axes.  Rocks range from unmetamorphosed but highly indurated to local well
Cretaceous? and Jurassic
Only fossil is Buchia mosquensis(?) of Late Jurassic age.
KJf
Kuskokwim Formation, undivided
Sandstone and siltstone
KJsh
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- siltstone, argillite, and shale
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- siltstone, argillite, and shale containing important but subordinate beds of volcaniclastic sandstone.  Inferred on basis of Eakins and others (1978).
Cretaceous or Late Jurassic?
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- siltstone, argillite, and shale containing important but subordinate beds of volcaniclastic sandstone.
Late Jurassic?
Possible belemnoid at one locality
KJh
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- hornfels
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- dark gray, locally gossanized, massive, hornfelsed KJs and KJsh, contains some spotted phyllite and numerous unmappable dikes.
Sandstone, siltstone, shale, and conglomerate
Kuskokwim Group sedimentary rocks
Sandstone, siltstone, shale, and conglomerate (Added, not in source)
Marine sedimentary sequence consisting of graywacke, sandstone, conglomerate, siltstone, and shale.
Early Cretaceous (Albian) age assigned from fossils found north of the map area.
h
Hornfels
Contact metamorphic zones adjacent to igneous intrusive rocks.
Metamorphic
s
Interbedded graywacke and shale, with local interbeds of argillite and conglomerate.
Inferred to be Kuskokwim Group consisting of sandstone, siltstone, shale, and conglomerate
Fine- to medium-grained often micaceous gray greywacke or silty greywacke.  Occasionally crossbedded, or with siltstone partings.  Rare argillite pebbles
Kka
Kuskokwim Group, nearshore facies
Kkn
TA008
Sandstone, siltstone, shale, and conglomerate.   Inferred from Platt and Muller (TA002) and Hoare and Condon (TA019)
KJm
McHugh Complex
Weakly metamorphosed siltstone, graywacke, arkose, and conglomeratic sandstone; greenstone (mostly basaltic), metachert, and argillite
Cretaceous and (or) Jurassic
Kmx
KPmc
McHugh Complex, basalt and chert
Pillow and massive basalt, depositionally overlain by radiolarian chert.
Early Cretaceous (Albian) to Middle Triassic (Ladinian)
Cretaceous to Triassic radiolaria in bedded chert
KPms
McHugh Complex, graywacke and conglomerate
Fault-bounded slices of massive conglomerate and graywacke.
Early Cretaceous to Early Jurassic (Pliensbachian)
Pliensbachian radiolaria in underlying ribbon chert
KPm
McHugh Complex, undivided
Complexly deformed tectonic assemblage of diverse lithologies (melange).  Lithologies include argillite, tuff, graywacke, basalt, chert, outcrop-scale melange, conglomerate, gabbro, and limestone.  Rocks typically show prehnite-pumpellyite facies metamor
Cretaceous to Permian
Permian conodonts and fusilinids.
Tectonite
Volcanogenic sedimentary rocks
Volcanogenic sedimentary rocks.
Tvep
Kkv
Tuff and related rocks
Tuff, some cherty argillite, minor limestone and locally, dikes extrapolation by inferrence from Hoare and Condon notes
Cretaceous?
Tuff, some cherty argillite, minor limestone and locally, dikes
Kd
Intermediate dike
Basalt-andesite dike intruding McHugh Complex.  Stored in coverage as arcs, arc-code = 50 and arc-para1 = 5
Early Cretaceous
Ar-Ar hornblende plateau age of 115 Ma
Ku
Kg
Ki7
Cretaceous intrusive rocks -- Unit 7 Granodiorite
Medium-grained, medium-gray hypidiomorphic-granular granodiorite.  Hornblende domination mafic, shows varying degrees of alteration.  Biotite locally present.  Locally cataclasis/mylonization.
Kgd
Ki10
Cretaceous intrusive rocks -- Unit 10 Granodiorite
Medium-grained seriate, whitish-gray granodiorite.
IL009
Grandoirite?
Granitic rocks associated with the Pebble Copper deposit
Dates between 89 and 100 Ma
Ki1
Cretaceous intrusive rocks -- Unit 1 Granodiorite
Light- to medium-gray, medium-grained, seriate, hypidiomorphic granular granodiorite.
Ki2
Cretaceous intrusive rocks -- Unit 2 Quartz monzodiorite
Medium- to coarse-grained, locally foliated composite pluton cheifly of hornblende-biotite quartz monzodiorite.  Possibly the same pluton as unit Ki3, LC002.
Ki3
Cretaceous intrusive rocks -- Unit 3 Quartz monzodiorite
Medium- to coarse-grained, medium-gray hornblende-biotite quartz monzodiorite.  Possibly same pluton as Ki2, LC002.
Ki9
Cretaceous intrusive rocks -- Unit 9 Granodiorite
Ranges from silicic granodiorite to mafic tonalite and quartz diorite.  Medium-grained, seriate and many show weak to strong cataclasis (probably mylonitic from description).  Some have subvertical, northeast trending primary foliation.
Kgdc
Ki11
Cretaceous intrusive rocks -- Unit 11 Granodiorite
Medium- to coarse-grained subporphyritic granodiorite.
Ki13
Cretaceous intrusive rocks -- Unit 13 Granodiorite
Primarily granodiorite but includes some granite.  Notably, is generally coarse-grained.  Low color index, biotite primary mafic, with traces of hornblende and muscovite in all examined thin-sections.
Medium- to coarse-grained subporphyritic granodiorite.  Polygons added based on air photo interpretation of scoured bedrock
Ki12
Cretaceous intrusive rocks -- Unit 12 Quartz diorite
Locally foliated, seriate hornblende-biotite quartz diorite.  Biotite-hornblende rationis quite variable although color index remains constant.  Deuteric epidote common.  Extension from adjacent Lake Clark quadrangle
Ki4
Cretaceous intrusive rocks -- Unit 4 Quartz diorite
Composite igneous mass that includes hornblende-pyroxene gabbro and diorite, quartz diorite, tonalite, and minor granodiorite.  Quartz diorite is the most abundant rock type and is medium- to coarse-grained, locally foliated, seriate and has more hornble
Kqd
Ki5
Cretaceous intrusive rocks -- Unit 5 Quartz diorite
Mafic igneous rocks, chiefly quartz diorite.  Medium- to locally coarse-grained and having a well developed primary subvertical foliation that trends northeat.  Most samples show cataclasis (mylonization?), which is pronouced near the shear zone in south
Ki6
Cretaceous intrusive rocks -- Unit 6 Quartz diorite
Slightly foliated, medium-grained, seriate, hornblende-biotite quartz diorite.
Locally foliated, seriate hornblende-biotite quartz diorite.  Biotite-hornblende rationis quite variable although color index remains constant.  Deuteric epidote common.
Ki8
Cretaceous intrusive rocks -- Unit 8 Granite
Coarse-grained, subporpyritic granite.  Part of a granite body exposed to the south in Iliamna quadrangle.
Kgk
Potassic granitic rocks of the Okstukuk Hills
Okstukuk Hills, biotite granite or syenite having very coarse feldspar laths, medium-grained very fresh biotite and fine-grained clinopyroxene
Ar-Ar total fusion age 84.49 +/- 0.05 biotite
Kqm
Massive, coarse-grained light-gray porphyritic quartz monzonite.
K-Ar age on co-existing biotite and hornblende yielded 80.7 and 83.4 Ma and hornblende yielded 74.1 Ma
Ki15
Cretaceous intrusive rocks -- Unit 15 Quartz monzonite
Fine- to medium-grained hypidiomorphic seriate quartz monzonite.
K-Ar age on hornblende is "Late Cretaceous"
Ki14
Cretaceous intrusive rocks -- Unit 14 Granodiorite
Porphyritic granodiorite having phenocrysts of quartz, plagioclase, biotite, and glomeroporphyritic clusters of pale-green amphibole in a groundmass of quartz and mostly potassic feldspar.
K-Ar age on biotite is "Late Cretaceous"
Called granodiorite tentatively based on mode.  Chemistry suggests diorite probably -- most similar to diorite field of LeMaitre (1976).  More probably proper name might be quartz diorite.
40/39 age of 75.22 Ma
KJv
Valdez Group (?)
Metawacke, metasiltstone, and argillite; locally phyllitic
Cretaceous and Jurassic (?)
Kvs
Kv
Valdez Group
Thick sequences of drab, rythmically alternating multiply deformed turbidites, including metasandstone, metasiltstone, argillite, slate, and phyllite, and rare beds of pebbly argillite and metasandstone;  generally beds are a few centimeters to a few met
Maestrichtian and Campanian(?) Inoceramus
Kvm
Melange of Iceworm Peak
Tectonic melange consisting of blocks of graywacke in a phacoidally cleaved matrix of slate having a Valdez Group protolith.
KCg1
Gemuk Group -- clastic rocks
Primarily coarse-grained clastic rocks containing some fine-grained cherty and volcanic material.
Probably Cretaceous to Triassic
Early Cretaceous (Valanginian), Jurassic, and Triassic
KJsv
KJvs
DI007
Togiak-Tikchik Complex mixed clastic rocks
Primarily coarse-grained clastic rocks containing some fine-grained cherty and volcanic material.  Highly contorted bedding common
Argillite and graywacke
Cretaceous to Jurassic
Interbedded graywacke and shale, with local interbeds of argillite and conglomerate.  In this quadrangle (D-8), most certainly includes rocks of the Gemuk Group and to a lesser extent Kuskokwim Group.  Includes, based on Hoare and Condon notes of 1969 an
Mzgg
Greywacke, greenstone, chert, and limestone
Calcareous argillic greywacke, greenstone, chert, cherty argillite, limestone, and greenschist
Mesozoic?
KJsvi
Calcareous argillic greywacke, greenstone, chert, cherty argillite, limestone, and greenschist apparently cut by dike swarms or shallow intrusions.  Unit inferred from air-photos
Jk
Graywacke and conglomerate
Typically dark-green or gray massive sandstone, although coarse-pebble conglomerate is locally present.  Rare fragmentary fossils are found within map area; a sample we collected in 2001 yielded fragments of Buchia, suggesting a Late Jurassic or Early Cr
Middle to Late Jurassic?
Rare fragmentary fossils, appearing to be possibly Buchia.  Reported Jurassic fossils found by Unocal in 1959.
Jkw
Sedimentary rocks, undivided
Dark-gray to green lithic metagraywacke, polymicitc conglomerate, and argillite are main rock types.  All are low-grade metamorphic, ranging from prehnite-pumpellyite to greenschist facies.  Argillite and siltstone facies show evidence of turbidite depos
Jurassic or Cretaceous
Nearly identical suite in the Nushagak Bay quadrangle yielded Middle Jurassic fossils, however a Cretaceous age can not be ruled out for the rocks in the Iliamna quadrangle (Graywacke of Kulukak Bay, NSA = 3140).
KJkr
LC003
Koksetna River sequence
Complexly deformed volcanic-lithic turbidites.  Consists of thick monotonous sequence of thin sandstone interbedded with pelagic shale.  Coarse, unsorted and chaotic matrix-supported conglomerate occurs sporadically
Early Cretaceous (Valanginian) to Late Jurassic (Kimmeridgian)
Two fossils reported, late Jurassic (Kimmeridgian) and Early Cretaceous (Valanginian)
Small area shown as KJs by Wallace and the extension of map unit KJs from the Iliamna map to the south.  Assigned to unit KJkr.  Also includes a single polygon in southwest part of quadrangle that is extension of unit KJs of the Iliamna quadrangle.  Pres
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- sandstone
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- volcaniclastic sandstone containing important but subordinate beds of siltstone and shale and minor beds of granule conglomerate.  Inferred on basis of Eakins and others (1978).
Jura-Cretaceous flysch, southern part of Kahiltna terrane
Cretaceous and Jurassic
KJkr?
Koksetna River sequence?
Flysch sequence, undivided
Flysch sequence, undivided, hornfels
Interbedded marine volcaniclastic sandstone, siltstone, and shale -- volcaniclastic sandstone containing important but subordinate beds of siltstone and shale and minor beds of granule conglomerate.
Probable Buchia mosquensis at one locality
Presence inferred on the basis of similar rocks in Dillingham quadrangle to the south and the Lake Clark quadrangle to east.  Fossil collections by UNOCAL geologists in 1959, originally reported as being in the Dillingham quadrangle were most likely from
Olivine basalt flows and fragmental mafic volcanic rocks-Ranges in apparent composition from andesite to basalt based on field calls.  Part of unit KJvs volcanic and sedimentary rocks; mapped separately only locally.
Volcanic and sedimentary rocks
Thick marine unit consisting of volcanic and sedimentary rocks.  Volcanic rocks range in composition from mafic pillow basalts to more abundant andesitic and trachytic flows, tuff, and breccia.  Interbedded with the volcanic rocks are tuffaceous siltston
Early Cretaceous to Middle Jurassic
Radiolaria of Late Jurassic to Early Cretaceous age, and fragmentary ammonites of Jurassic age.
Thick marine unit consisting of volcanic and sedimentary rocks.  Volcanics range in composition from mafic pillow basalts to more abundant andesitic and trachytic flows, tuffs, and breccias.  Interbedded with the volcanic rocks are tuffaceous siltstone,
Low-grade metamorphic or contact metamorphosed volcanic and lesser sedimentary rocks.  Altered volcanic breccia is relatively abundant; however in the southwestern part of T.4 S., R.40 W., unit consists largely of vertically standing beds of contact-meta
Radiolaria of Late Jurassic to Early Cretaceous age and fragmentary ammonites of Jurassic age have been collected from this unit in the Goodnews Bay quadrangle to the west (Hoare and Coonrad, 1978)
Granodioritic rocks
Granodiorite and quartz diorite
Age assigned revised based on Nelson and others (1983)
KJi
Cretaceous(?) and Jurassic(?) intrusive rocks -- Quartz monzodiorite
Medium-gray, medium-grained, hypidiomorphic granular hornblende-biotite quartz monzodiorite containing variable amounts of clinopyroxene.  Flow structures locally present and hornblende and plagioclase is aligned in a north-northeast direction.
Cretaceous? and Jurassic?
K-Ar biotite and hornblende ages ranging from 57.4 to 95.1 Ma
KJg
Js
Sedimentary rocks, undifferentiated
Jurassic
J
Jurassic sedimentary rocks
Jsu
Jn
Naknek Formation
Arkose, conglomerate, sandstone, siltstone, and shale
Late Jurassic  (Oxfordian to Tithonian)
Ammonites and pelecypods, especially Buchia which provides tight age control
Sandstone, arkose, conglomerate, and siltstone
Late Jurassic
Late Jurassic (Oxfordian to Kimmeridgian)
Jnss
Naknek Formation, lower sandstone member
Thin-bedded to massive arkosic sandstone, graywacke, and siltstone, mainly restricted to central part of region
Jnn
Jns
Naknek Formation, Snug Harbor Siltstone Member
Massive to thin-bedded dark-gray to black siltstone; laminated near base
Jnp
Naknek Formation, Pomeroy Arkose Member
Massive light-gray arkose and arkosic conglomerate; minor interbeds of siltstone
Jni
Jnc
Naknek Formation, Chisik Conglomerate Member
Massive cobble-boulder conglomerate, mainly restricted to area adjacent to Iniskin Bay and Tuxedni Bay
Jcp
Chinitna Formation, Paveloff Siltstone Member
Massive to thin-bedded gray arenaceous siltstone, weathers gray, large ellipsoidal concretions and lenticular beds of limestone, massive sandstone unit at base
Jc
Chinitna Formation
Primarily dark-gray to brown massive arenacous siltstone containing a few sandstone interbeds and numerous limestone concretions.  Unit is subdivided into members, however not on this map
Middle Jurassic (Callovian)
Abundant fossils, including many species of ammonites:  Cadoceras, C. stenocadoceras, C. pseudocadoceras, Kepplerites, Kheraiceras, Lilloettia, and Gowericeras.  Also especially known for Iniskinites and Chinitnites
Siltstone, limestone concretions, and sandstone
Late Jurassic (Callovian)
Jct
Chinitna Formation, Tonnie Siltstone Member
Massive to thin-bedded brownish-gray arenaceous siltstone, weathers red-brown, small yellowish-brown limestone concretions in parallel bands, minor sandstone at base
Graywacke of Kulukak Bay
A thick marine sedimentary unit referred to as "Weary graywacke" by Hoare and others, 1975.  Consists of very hard graywacke and siltstone with local conglomerate.
Middle to early Late Jurassic
Buchia, Inoceramus, belemnites, and rare ammonite fragments ranging from Middle to early Late Jurassic age.
A thick marine sedimentary unit referred to as "Weary graywacke" by Hoare and others, 1975.  Mapped in the eastern part of the quadrangle by correlation with unit KJs of the adjacent Iliamna quadrangle.  Typically consists of dark green or gray massive s
Jt
Tuxedni Group
Light- to dark-gray and green graywacke, conglomerate, siltstone, and shale.  Graywacke ranges from feldspathic to lithic to laumontitic; conglomerate composed mainly of volcanic clasts in a graywacke matrix.  Unit is subdivided into Formation, however n
Middle Jurassic (Bajocian and Bathonian)
Abundantly fossiliferous, containing ammonites and pelecypods.  Key ammonites include Erycites, Tmetoceras, Sonninia, Stemmatoceras, Emileia, Stephanoceras, Chondroceras, and many others
Jtx
Tuxedni Formation
Sandstone, siltstone, and limy concretions
Middle Jurassic
Jtu
Middle to Late Jurassic (Bajocian to Callovian)
Jtb
Tuxedni Group, Bowser Formation
Heterogeneous assemblage of sandstone, conglomerate, shale and siltstone characterized by rapid facies changes.  Massive light- to dark-gray sandstone and conglomerate are the dominant lithologic types on the Iniskin Peninsula.  The sandstone and the con
Middle and Late Jurassic
Abundantly fossiliferous, containing ammonites and pelecypods, the units can be divided into two faunal zones which correspond to the break between the Middle and Upper Jurassic.  The lower faunal zone immediately overlies the unconformity with the Twist
Jtt
Tuxedni Group, Twist Creek Siltstone
Soft, poorly consolidated, thin-bedded to massive siltstone and silty shale as much 125-m-thick.  The siltstone is dark-gray, weathering to dark-rusty brown and contains many thin beds of volcanic ash that weather a bright orange color.  Small limestone
Abundant ammonite fauna which includes Oppelia (Liroxyites), Megasphaerceras, Leptoshinctes, Lissoceras, and Normannites (Dettermanites)
Jtc
Tuxedni Group, Cynthia Falls Sandstone
Massive to thick-bedded graywacke sandstone and pebble conglomerate about 200-m-thick.  The sandstone is medium- to coarse-grained, greenish-gray to dark-green, weathering mottled light-gray due to zeolites and has graded bedding.  The sandstone consists
The sparse fauna includes the ammonites Chondroceras and Stephanoceras as well as the pelecypods Inoceramus sp. and Mytilus sp.
Jtf
Tuxedni Group, Fitz Creek Siltstone
Thick sequence of massive, bluish dark-gray, arenaceous coarse- to fine-grained siltstone that commonly weathers rusty orange and contains many small limestone concretions.  Interbedded are fine-grained sandstone and, locally, conglomerate interbeds.  In
This unit is abundantly fossiliferous and is the first unit of the Tuxedini Group where ammonites are more numerous than pelecypods.  A few non-diagnostic brachiopods are also present.  The ammonites include Normannites, Teloceras, and Chondroceras and m
Jtg
Tuxedni Group, Gaikema Sandstone
Resistant, cliff-forming, massive to thin-bedded graywacke sandstone and cobble conglomerate showing graded bedding.  Conglomerate is confined to the Iniskin Peninsula, clasts in it consist of red and green felsic volcanic rocks, aphanitic igneous rocks
Fossiliferous throughout, containing pelcypods Meleagrinella, Trigonia, and Inoceramus and ammonites Witchellia(?), Stephanceras and locally, Sonninia (Papilliceras), Lissoceras, and Emileia
Jtr
Tuxedni Group, Red Glacier Formation
Thin-bedded to massive, red-brown weathering dark-gray to moderate olive-gray siltstone in the concentrated in the upper part of the unit and consisting of about 40 percent of the Formation.  The siltstone is highly arenaceous and locally contains lentic
The Red Glacier Formation is most abundantly fossiliferous in its upper parts, no fossils are known from the lower 2000 feet of the unit.  Pelcypods include Meleagrinella, Trigonia, Inoceramus, Camptonectes, and Pleuromya.  Ammonites occur in two distinc
Jlvs
Marine unit of mafic flows, some pillow structure, volcanic breccias, and massive fine- to medium-grained volcanogenic sedimentary rocks.  Fractures commonly coated with laumontite
Early Jurassic
Weyla pelecypods of Early Jurassic age.
JTrtk
Jtk
Talkeetna Formation
Mainly volcanic breccia, agglomerate, lava flows, and tuff.  Sedimentary rocks locally interbedded but are minor.  Informally divided into three members, which correlate with formal members elsewhere.
Early Jurassic -- Sinemurian to Pliensbachian
Nondiagnostic in Iliamna quadrangle, good fossils known from northern exposures in Talkeetna Mountains.
Jtku
Talkeetna Formation, undivided
Tuff, sandstone, agglomerate, breccia and some lava flows
KJu
Metasedimentary rocks (undivided)
Weakly metamorphosed slate and graywacke; locally includes volcanic and intrusive rocks, undivided.  Consists of contact metamorposed Talkeetna Formation according to Detterman and others (1976, KN010).
KJfm
Volcanic breccia, tuff, agglomerate, and aphanitic lava flows; as mapped, locally includes Kamishak Formation in Ilianna Quad
bpT
Jurassic bedrock
Volcanic flows, tuffs, and breccias, metamorphic equivalents, and granodiorite.  Talkeetna Formation and other units
Jv
Volcanic rocks, locally includes sedimentary rocks
Mz
KN010
Metamorphic rocks
Schist, hornfels, and amphibolite, contact metamorphosed Talkeetna Formation
Mesozoic
sv
Sedimentary and volcanic rocks
Cheifly Jurassic volcanic rocks; locally includes Mesozoic and Cenozoic sedimentary and volcanic rocks
Cenozoic and Mesozoic
JTr
Talkeetna Formation?
Jurassic volcanic and volcaniclastic rocks
Jurassic and Triassic
Mainly volcanic breccia, agglomerate, lava flows, and tuff.  Sedimentary rocks locally interbedded but are minor.  Informally divided into three members, which correlate with formal members elsewhere.  Includes informally named Pogibshi Formation on east
Early Jurassic (Hettangian to Toarcian)
Jtkh
Talkeetna Formation, Horn Mountain Tuff Member
Mottled andesitic tuff, tuffaceous sandstone, and siltstone, locally contains andesitic flows
Jtkp
Talkeetna Formation, Portage Creek Agglomerate Member
Massive pink agglomerate and some volcanic breccia; minor andesitic flows, locally metasedimentary rock
Jtkm
Talkeetna Formation, Marsh Creek Breccia Member
Massive green volcanic breccia, lava flows, in part of submarine origin, interbedded with argillite and meta tuff, low rank metamorphism mainly confined to lower part
MzPzgps
Phyllite argillite, and chert
Gray to black phyllite or slaty argillite, occasionally calcareous or sulfide-bearing along fault zones
Early Jurassic or Late Triassic?
Age based on Box and others (1993) Bethel map, Early Jurassic radiolarians
Trondhjemite
Medium- to coarse-grained, light-gray muscovite bearing trondhjemite
K-Ar muscovite age of 145 Ma
Jth
Trondjemite
Ji2
Jurassic intrusive rocks -- Unit 2 Trondhjemite
Medium- to coarse-grained, seriate, leucocratic trondhjemite
A sample from the Iliamna quadrangle yielded a 145 Ma K-Ar age on muscovite
Jg
Granitic rocks of the Alaska-Aleutian Range batholith
Jurassic granitic rocks
Jqd
J(?)f
Felsite
Fine-grained aphanitic, light gray felsite
Jurassic? or early Tertiary?
Jgr
Jqm
Medium-grained, light-gray with a pinkish cast quartz monzonite, locally includes granodiorite and trondhjemite.
Jgd
Medium- to coarse-grained pink to gray granitic-textured quartz monzonite
p
Pegmatite or aplite dikes
Ji3
Jurassic intrusive rocks -- Unit 3 Granodiorite
Whitish-gray, medium-grained, seriate biotite granodiorite.
pg
Pink quartz monzonite dikes
Quartz diorite
Medium- to coarse-grained, light-gray quartz diorite that contains biotite and hornblende, locally includes small areas of diorite and granodiorite.
Multiple K-Ar ages ranging form 168 Ma on hornblende to 152 Ma on biotite.  Analytically best ages cluster around 155 to 158 Ma
Mainly biotite-hornblende-quartz dioriite
Jqt
Quartz diorite, diorite, and granodiorite
Ji1
Jurassic intrusive rocks -- Unit 1 Tonalite
Medium-grained tonalite and quartz diorite, locally foliated.  Two small exposures of gabbro and diorite included in unit.
di
Quartz diroite dikes
Quartz diorite dikes
Ju
Plutonic rocks, undivided; chiefly tonalite and trondhjemite
JT
Tonalite
Tonalite, includes hornblendite, hornblende-biotite quartz diorite, and rare granodiorite, quartz monzonite, and granite
Jd
Diorite of Point Bede
Fine- to medium-grained nonfoliated quartz diorite.
Jurassic?
Jto
Tonalite of Dogfish Bay
Medium-grained nonfoliated tonalite.
Medium- to coarse-grained diorite, locally includes small areas of quartz diorite and gabbro; numerous xenoliths.
Jmu
la
Lamprophyre dikes
Ji
b
Basalt dikes
mi
Mafic igneous rocks
Predominantly diabase, probably intrusive.  Associated with silicious sedimentary and extrusive rocks of now abandoned Gemuk Group of questioned Jurassic age.
Jvab
Jm
Mafic and ultramafic plutonic rocks
Gabbro, hornblende gabbro, hornblendite, and pyroxenite
K-Ar age of 183 Ma on hornblende
Jsm
Seldovia metamorphic complex
Marble, quartzite, garnet-mica schist, and glaucophane-bearing amphibolite
191.1 and 191.7 Ar-Ar on white mica and 191.9 Ar-Ar on hornblende
Jsch
eJTrl
Limestone, shale, and chert
Cream colored to dark-gray, limestone, shale, and chert.
Early Jurassic? and Triassic -- Norian
Triassic (Norian) fossils collected by Blodgett amd Blome
Trgl
Gemuk Group, limestone and chert
Interbedded limestone, fossiliferous argillaceous limestone, and gray-green chert
Triassic
Monotis and Halobia
Trlc
Triassic limestone and chert
Cream colored to dark-gray, limestone, and chert, locally interbedded in thin repeating beds.
Triassic (Norian)
Trk?
Trlt
Limestone
Newly described limestone, faunally distinct from limestone and chert section.  Only known from the TA D-2 and D-3 quadrangles
Relatively abundant fauna, to be described
Trk
Kamishak Formation
Limestone, grey to black chert, and porcellanite
Late Triassic
St
Highly fractured dark-gray limestone and chert
Silurian
Contains stromatoporoids (undet.), solitary rugose coral, Pentameris(?) sp. and undet. rynchonelloid brachiopods at one fossil locality
JTrp
Port Graham Formation of Kelley (1980)
Dark-gray, carbonaceous limestone and silty limestone, also includes tuff, tuffaceous sedimentary rocks, and chert.  Most of unit considered Norian in age.
Early Jurassic and Late Triassic
Bivalves of Late Triassic (Norian) age
JTrta
Trku
Kamishak Formation -- Ursus Member
Thin-bedded, light-gray limestone (locally dolomitic), and minor interbedded gray chert and porcellanite and minor tuff.  Limestone is fine-grained biomicrite.  Depositional environment was moderate to high-energy, shallow water.  Unit cut by abundant di
Late Triassic? or Early Jurassic?
None definitive
Trkm
Kamishak Formation -- Middle Member
Thin- to medium-bedded, dark-gray to black limestone and calcilutite (locally dolomitic), and minor black chert and gray tuff.  Limestone is fine-grained microsparite.  Calcite is locally altered to chert, suggesting a deep-basin environment.  Unit cut b
Late Triassic (middle to late Norian)
Corals: Koilocenia cf. K. andreai (Volz), Oppelismilia cf. O. mojsvari (Frech), and Thamnasteria sp.; hydrozoan Heterastridium cf. H. conglobotum Reuss and Monotis subcircularis Gabb
Trkb
Kamishak Formation -- Briun Limestone Member
Massive to thin-bedded, light- to dark-gray limestone; coral and echinoid bioherms, banded green and white chert.  Environment was apparently high energy, shallow water.  Unit cut by abundant dikes and sills either related to the Cottonwood Bay Greenston
Late Triassic (Norian)
Halobia cf. H. dilatata and Monotis(?) sp.
KCg2
Gemuk Group -- Triassic limestone
Generally white to cream colored, recrystallized limestone, however locally is dark gray and only finely crystalline.  Possibly fault bounded occurrences.
Triassic (Norian) fossils collected by Mertie
Trvs
Marine unit consisting of chert, tuffaceous cherty rocks, argillite, siltstone, volcanic wacke, conglomerate, limestone, and mafic flows and breccias.
Pelecypods of Late Triassic age
Trcg
Trsh
Gray shale and gray volcaniclastic sandstone
Gray shale and gray volcaniclastic sandstone.  Inferred on basis of Eakins and others (1978).
Ssh
Trb
Volcanic rocks within former Gemuk Group.  Inferred from extrapolation of Hoare and Condon field notes.
KTrPCg
TA017
Gemuk Group -- basalt
Volcanic rocks comprising at least 5 separate flows, locally as much as 200 feet think interbedded with cherty siltstone.  Thought to occur stratigraphically near top of Gemuk section.
Associated Monotis and Halobia, late Triassic
Trv
Predominantly basaltic flows and volcaniclastic rocks.  May be equilvalent to the Chilikadrotna Greenstone of Triassic age.
Jurassic? or Triassic?
Trc
Cottonwood Bay Greenstone
Dark-gray to dark-green porphyritic to amygdaloidal basaltic flows altered to greenstone.  In general, slightly more metamorphosed than Nikolai Greenstone.
Late Triassic (pre-Norian?)
Sc
Chilikadrotna Greenstone
Basalt, andesite, chert, limestone, and tuffaceous sedimentary rock, all weakly metamorphosed.  About 60 percent of unit is metabasalt
Unit originally assigned a Silurian age, was later found to be in error and is now considered Triassic.
JTrv
Basaltic pillows and flows, andesitic breccia, chert, and limestone.
Sg
Greenstone, dark-green basalt
Dark-green basalt having relict pillow structures, containes minor red and balck chert.  Inferred on basis of Eakins and others (1978).
JTrca
JTrca?
Trcb
Greenstone
Trcb + MzPzp
Cottonwood Bay Greenstone and ?
Greenstone and ?
Trcb?
Dark-green basalt having relict pillow structures, containes minor red and balck chert
Spb
Greenstone, purple basalt
Purple basalt and hematite rich sandstone
Predominantly mafic flows and volcaniclastic rocks.  May be associated with the Chilikadrotna Greenstone of Triassic age from the Lake Clark quadrangle.
Triassic?
KCg
Gemuk Group -- undivided
MzPzgs
Contact metamorphic zones adjacent to igneous intrusive rocks.  (Note, in this quadrangle, probably includes both Kuskokwim and Gemuk units, hence source rock are in part older than Cretaceous).
Interbedded graywacke and shale, with local interbeds of argillite and conglomerate.  In this quadrangle, most certainly includes rocks of the Gemuk Group and to a lesser extent Kuskkwim Group.
Trg
Gemuk Group, undifferentiated
Graywacke, siltstone and lesser amounts of chert, tuff, shale, and black limestone
Trgv
Gemuk Group, sedimentary and volcanic rocks
Graywacke, siltstone, and volcanic rocks, including lava and tuff, interbedded with black shale, black limestone, argillaceous limestone, and chert
Mg
Gabbro
Dark-green, medium- to coarse-grained gabbro and minor leucogabbro and plagiogranite.  Associated with McHugh Complex as fault-bounded bodies.
Mzm
Mu
Ultramafic plutonic rocks
Predominantly layered, variably serpentinized dunite containing rare to locally abundant layers of chromitite and pyroxenite and fault slices of garnet pyroxenite and serpintinite.  Associated with McHugh Complex as fault-bounded bodies.
Mzum
KCg4
Gemuk Group -- Mississippian(?) rocks
Consists of massive and thin-bedded chert interbedded with siltstone and graywacke (generally calcareous), thin-bedded limestone, and minor mafic volcanic rocks.  Chert is black, white, and gray and specifically not green, which is characteristic of youn
Mississippian?
MzPzm
MzPz
Mesozoic and Paleozoic rocks, undivided
Thick, widespread, marine unit consisting of volcanic and sedimentary rocks ranging in age from Early (?) Ordovician to Early Cretaceous.  Unit consists of thin-bedded to massive tuffaceous cherts and siltstones, argillite, graywacke, pebble-cobble congl
Early Cretaceous to Early? Ordovician
Limestones commonly contain Permian fossils
Limestone commonly contains Permian fossils
Predominantly graywacke, fractured argillite, and chert (undivided)
Melange
Two or more rock types occuring in close proximity, typically tightly folded, sheared, and/or altered, including basalt (+/- pillows), gabbro, greywacke, shale, siltstone, limestone, and dolomite.
Gemuk Group -- massive coarse-grained clastic rocks
Massive, coarse-grained sandstone, quartzite, and conglomerate.
TrDs
Gemuk Group -- bedded clastic rocks
Well-bedded, fine-grained sedimentary rocks, based on airphoto interpretation.
MzPzp
Metamorphic rocks?
Mesozoic and Paleozoic
MzPzs
Biotite-feldspar-quartz schist
Biotite-feldspar-quartz schist, locally actinolite-feldspar-quartz schist or garnet-feldspar-quartz schist.
Jmg
Migmatite
Admixture of intrusive and metamorphic rocks, grading from gneissic to schistose texture, exposed along east margin of Alaska-Aleutian Range batholith.
Middle and Early Jurassic
JPk
Kakhonak Complex
Exposed chiefly as roof pendants in Alaska-Aleutian Range batholith and consists of schist, gneiss, quartzite, marble, phyllite, argillite, and slate.  Greenschist facies metamorphic grade.  Metamorphic rocks are thought to equivalent to Jurassic and Tri
Jurassic, Triassic, and Permian?
JPzk
Trm
Metamorphic rocks, undivided
Metalimestone, argillite, quartzite, metatuff, greenstone, and phyllite; may in part be equivalent to the Kamishak Formation
Late? Triassic
Metamorphic rocks, undifferentiated
as
Amphibolite
Amphibolite, locally includes sedimentary rocks
early Mesozoic?
TrPztc
Tlikakila Complex
A diverse complex of metamorphosed and highly deformed rocks, whose protoliths include calcerous to siliceous clastic rocks, limestone, thin-bedded chert, massive basalt, massive to layered gabbro and pyroxenite, and ultramafic rocks.  Most of complex me
Triassic to Paleozoic
Late Triassic megafossils and conodonts from limestone; clearly a protolith age.
LC004
A diverse complex of metamorphosed and highly deformed rocks, whose protoliths include calcerous to siliceous clastic rocks, limestone, thin-bedded chert, massive unpillowed basalt, massive to layered gabbro and pyroxenite, and serpentinized ultramafic r
TC
Complex assemblage of metamorphiosed and hornfels(?) volcanic and sedimentary rocks
Jurassic and older?
Metamorphosed mafic volcanic rocks, phyllite, schist, quartzite, marble, calc-silcate rocks, serpentinite, gabbro, and chert
Metamorphosed mafic volcanic rocks, phyllite, schist, quartzite, marble, calc-silcate rocks, serpentinite, gabbro, and chert.  Mixed unit of varying affinity and protolith and metamorphic age.  Dominant rock of unit is metamorphosed mafic volcanic rocks
MzPzb
Mafic metamorphic rocks?
Mafic rocks?
M
ePzc
Black chert
Predominantly of black and gray chert but also includes rare white, buff, red, or green bedded to massive chert.  It is occasionally vitreous, banded or fractured, and is interbedded with minor amounts of limestone, amygdaloidal basalt, and thin pitted c
Ealry Paleozoic
Hoare and Jones (1981) report Lower Paleozoic (Devonian? and pre-Devonian) and Paleozoic(?) radiolarians from this unit as well as Permian megafossils.
Pl
Thin, widespread, fine-grained, crystalline limestone.  Fetid odor.  Generally tuffaceous, locally cherty.
Permian
Pls
Reported brachipods and crinoids
Pcs
Clastic rocks
Predominantly fine to coarse-grained, rarely conglomeratic or brecciated, light gray, greenish-gray, or black streaky, slaty, phyllitic, micaceous or silty bedded to massive graywacke.  Cigar sized and shaped pits, boudins, or slightly hornfelsed in some
Permian?
Associated Permian limestone containing Atomodesma
KCg3
Gemuk Group -- Permian volcanic rocks
Predominantly dark-green to black, altered mafic volcanic rocks having abundant amygdules.  Volcanic breccia, calcareous tuff, and pillow lava constitute lower beds, pillow lavas in middle, and phyllitic calcareous tuff and tuffaceous limestone constitut
Permian? and Triassic?
Pv
Permian volcanic rocks
Mrc
Rainbow chert
Mostly highly deformed white, gray, red, and minor green or black, thin-bedded to massive chert.  It is locally banded or brecciated and interbedded with minor red siliceous shale, argillite, dolomitic limestone, greywacke, and rare red volcanic rocks an
Mississppian?
Associated and presumably overlying limestone has yielded Permian megafossils (Hoare and Jones, 1981).  One locality on the shore of Chikuminuk Lake yielded Triassic radiolaria, which is yet to be explained
Greenstone, phyllite, and schist
Fine- to coarse-grained greenstone, occasionally calcareous or schistose, rarely interbedded with green chert, argillite and tuff.  Gray to black phyllite or slaty argillite, occasionally calcareous or sulfide-bearing along fault zones.  Greenschist with
Mesozoic or Paleozoic
Sab
TA007
Algal boundstone
Thick to massive bedded, light gray algal boundstone, locally dolomitized; composed primarily of spongiostromate algal heads (including abundant oncoid forms).  Equivalent to Sl of Gilbert (1981)
Late Silurian (Ludlovian-Pridolian)
Aphrosalpingid sponges (notably Aphrosalpinx textilis Miagkova) locally common.  Moinr accessory brachiopods
Thick to massive bedded, light gray algal boundstone, locally dolomitized; composed primarily of spongiostromate algal heads (including abundant oncoid forms).  Inferred from air photos
Sls
Lime mudstone
Thin- to medium-bedded, laminated, dark gray to dark brown, platy lime mudstone, having strong petroliferous odor.  Coarse-grained limstone debris-flows having clasts of algal boundstone reef material common in uppermost part of unit; immediately below c
Late Silurian (Wenlockian)
Graptolites and conodonts
Spf
Olss
Tcherskidium-bearing limestone
Brown, medium- to thick-bedded skeletal lime packstone to wackestone.
Late Ordovician (Ashgillian)
Abundant pentameroid brachiopods (Tcherskidium and Proconchidium (or Ecconchidium))
Os
Shale
Extremely poorly exposed brown and gray 'chippy' shale, silty shale and silicified limestone
Ordovician
Ocs
Clastic rocks of middle Ordovician age
Middle Ordovician
Oab
Algal boundstone and lime mudstone
Medium- to thick-bedded, dark-gray to brown algal thrombolites (boundstone) interbedded with light-gray weathering thin- to medium-bedded lime mudstone.
Early Ordovician
Trilobites
Ols
Thin- to medium-bedded, yellow-gray weathering, dark-gray fresh, burrow mottled lime mudstone.  Peloidal mudstone locally common.
Gastropods and conodonts
Cls
Medium- to thick-bedded, commonly light-gray to dark-gray, rarely pink weathering (light-gray fresh) lime mudstone having locally abundant, well developed wavy styolites.  Minor green-gray shale intervals present locally.
Cambriam, middle
Trilobites locally abundant and diverse in this subunit and are indicative of a Mayan (late Middle Cambrian age
Limestone and siliclastic rocks
Thin-bedded platy limestone associated with coarse-grained siliclastic sandstone and granule comglomerate, possible shale.
Cambriam, middle or early
Pal
Holitna Group
Various types of limestone ranging from dense, fine-textured to more coarsely crystalline (recrystallized) types.  Recrystallized facies are partly dolomitic.  Massive limestone is predominant and forms prominent topographic features.  Thinly bedded vari
Devonian to Silurian
Predominatly stromatoporoids and corals but includes sponges, bryozoans, brachiopods, trilobites, and ostracodes.
DZn
DSab
Early Devonian to Late Silurian
ds
Dolostone
Paleozoic
Pzls
Marble
Hornfelsed carbonate rocks
Zs
Dolostone, limestone, orthoquartzite, and minor chert
Medium-bedded, medium-gray, orange weathering dolostone, limestone, orthoquartzite, and minor chert.  Dolostone has locally abundant floating quartz grains, is locally trough cross-stratified, but also has well developed parallel laminations, low domal s
Proterozoic
None reported