bu
Bedrock unknown
Areas of known or apparent bedrock exposures.  Bedrock type unknown.  In the Taylor Mountains quadrangle, a number of the areas shown as bedrock unknown are in areas mapped as largely Kuskokwim Group; however, on air-photos these areas appeared distincti
Wilson, F.H,, Blodgett, R.B., Blome, C.D., Mohadjer, Solmaz, Preller, C.C., Klimasaukas, E.P., Gamble, B.M., and Coonrad, W.L., in press, Reconnaissance bedrock geologic map for the northern Alaska Peninsula area, southwest Alaska, including the Dillingh
Qs
Surficial deposits, undivided
Quaternary
Unconsolidated, poorly to well-sorted, poorly to moderately well-stratified deposits; consist predominantly of alluvial, colluvial, glacial, marine, lacustrine, eolian, and swamp deposits.  Also, locally includes reworked volcanic debris as well as block
Qsb
Scoured bedrock
Quaternary?
Areas of glacially scoured unexposed bedrock covered by a thin(?) mantle of unconsolidated surficial deposits; air-photo interpretation.  Where shown, bedrock type is indeterminate from available data
Qv
Volcanic rocks, undivided
Andesite, dacite, and basalt lava flows, volcanic breccia, lahar deposits, and debris-flow deposits.  Includes air-fall tuff, volcanic dome deposits, block-and-ash-flow deposits, ash-flow tuffs, volcanic-rubble flows, debris flows and hot-blast avalanche
Hv
Volcanic rocks
Quaternary, Holocene
Andesite and basalt lava flows, and sills.  These primarily extrusive rocks typically form the present day edifices of Iliamna and Redoubt Volcanoes.  They cap ridges and include massive lava flows, agglomerate, and lahar deposits, primarily associated w
Qdf
Debris-flow deposits
Debris flow deposits from Redoubt Volcano in the Crescent River valley.  Includes several small (older?) deposits in the upper valley and a 3,500-year-old debris flow in the lower valley.  The older deposits are of multiple debris flows off the west and
Qmf
Volcanic rubble and mudflows
Volcanic rubble and mudflows on Augustine Volcano (Detterman and Reed, 1980) as well as mudflows in the Drift River valley draining Redoubt Volcano (Till and others, 1993)  these deposits are of Holocene age and many are historic including 1963 mudflows
Jtf
Tuxedni Group, Fitz Creek Siltstone
Middle Jurassic, middle Bajocian
Thick sequence (up to 400 m thick) of massive, bluish dark-gray, arenaceous coarse- to fine-grained siltstone that commonly weathers rusty orange and contains many small limestone concretions (Detterman and Hartsock, 1966).  Interbedded is fine-grained s
Qamp
Andesite and dacite domes
Composite dome complex of Double Glacier Volcano consisting of medium- to coarsely porphyritic hornblende andesite and dacite.  Three K-Ar whole-rock ages were determined on these domes, two are considered minimum ages at 627 and 763 ka and one yielded 8
QTv
Quaternary, Pleistocene or Tertiary, Pliocene
Detterman and Reed (1980) mapped two eruptive centers within the Jurassic part of the Alaska-Aleutian Range batholith in the Iliamna quadrangle.  Only one of the sites was examined and that only briefly by Detterman and Reed (1980).  Scoriaceous olivine
Ts
Sedimentary rocks
Tertiary, Pliocene or Miocene
Consists 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 (Detterman and Reed, 1980).  Micaceous clay and sil
Ttyh
Kenai Group, Tyonek Formation and Hemlock Conglomerate undivided
Tertiary, Miocene and Oligocene
Sandstone, conglomerate, and siltstone.  Known within the map area only in the vicinity of Harriet Point in the Kenai quadrangle, these rocks are inferred from the description in Detterman and others (1976) to consist of fluvial conglomeratic sandstone a
Tcl
Copper Lake Formation, undivided
Tertiary, Eocene and Paleocene?
Thick clastic nonmarine sedimentary rock unit consisting of an upper and lower conglomerate member bounding a middle sandstone and siltstone member (Detterman and Reed, 1980; Detterman and others, 1996) at the east end of Lake Iliamna.  Upper conglomerat
Twf
West Foreland Formation
Tertiary, Eocene
Tan to light-yellow-brown cobble conglomerate interbedded with lesser sandstone, laminated siltstone, and silty shale (Detterman and Hartsock, 1966).  Thin coal beds are interbedded with the siltstone and shale.  The clasts in the conglomerate are mainly
Tvu
Tertiary
Andesite, basalt, and dacite lava flows, tuff, lahar deposits, volcanic breccia, and hypabyssal intrusions.  Widely scattered throughout the map area, they are most apparent in the Lake Clark quadrangle where they are a subdivision of the Tvf map unit of
Tvr
Felsic volcanic rocks
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.  Much of this unit was included in map uni
Tb
Basaltic volcanic rocks
Late Tertiary
Olivine basalt lava flows as much as 10 m thick and locally diabasic intrusive rocks in the northwest corner of the Taylor Mountains quadrangle.  These columnar-jointed flows, which form a large tilted plateau, yielded K-Ar ages of 4.62 and 4.72 Ma (Reif
Tpg
Gibraltar Lake Tuff
Tertiary, Pliocene? to Oligocene?
Defined by Detterman and Reed (1980), it is divided into a lower welded member and an upper nonwelded member.  The upper member consists of light-gray to white crystal ash-flow tuff having a maximum thickness of 152 to 182 m.  It is locally capped by bas
Tmf
Tuffaceous felsic volcanic rocks
Tertiary, Oligocene and Eocene
Cream, light-gray, green, and purple bedded lithic, crystal, and vitric tuff; light-gray to tan welded crystal and lithic tuff most common (Detterman and Reed, 1980).  Also includes distinctive light colored horizons of felsic tuff interlayered with oliv
Tmv
Ranges from rhyolitic breccia, ash-flow tuff, and flows to dark-gray to green, coarse andesitic and basaltic volcanic rubble, lahar deposits, glassy to porphyritic basaltic andesite and andesite lava flows.  Includes minor volcaniclastic sedimentary rock
Tmba
Basalt and andesite
Dark-gray to green glassy to porphyritic basaltic andesite and andesite lava flows.  Also includes andesite to basalt plugs, volcanic rubble and breccia, including some agglomerate; may include deposits of lahars (Detterman and Reed, 1980).  Includes two
Tvig
Ignimbrite
Tertiary, Paleocene
Crystal tuff containing variable amounts of biotite and feldspar crystals in a tuffaceous matrix (Wilson and others, 2003).  Unit is widespread in the Stuyahok Hills in the northeast Dillingham quadrangle and varies in general appearance from crystal tuf
Tig
Granite and aplite
Tertiary, Oligocene? and younger
This map unit includes a variety of granite bodies in the Lake Clark quadrangle (Nelson and others, 1983).  A multiphase, hypabyssal leucocratic grayish-pink biotite granite outcropping north of the Lake Clark fault system (Ti13 of Nelson and others, 198
Ti
Intrusive rocks, undivided
Generally consists of fine- to medium-grained granodiorite and quartz diorite, but also includes granite (Nelson and others, 1983).  Typically surrounded by well-developed hornfels zones and sporadic hydrothermal alteration in country rocks, includes vol
Togd
Granodiorite and quartz monzodiorite
Tertiary, Oligocene and late Eocene
A compositionally variable suite of medium-grained, slightly foliated rocks ranging from tonalite to monzodiorite, including quartz diorite and granodiorite (Detterman and Reed, 1980; Nelson and others, 1983).  Also, heterogeneous, intensely sheared and
Teg
Granite
Tertiary, late Eocene
Largely granite, but includes lesser granodiorite and quartz monzodiorite (Nelson and others, 1983).  This map unit includes a large biotite granite, biotite-hornblende granite and granodiorite pluton in the northeast part of the Lake Clark quadrangle wh
Tipg
Older 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 Iliamna quadrangle.  Age inferred; however, a single K-Ar age (Reed and Lanphere, 1972
Tpgr
Peralkaline granite
Mostly medium-grained hypidiomorphic granular granite containing subhedral to euhedral perthite (Nelson and others, 1983).  Only peralkaline granite associated with Alaska-Aleutian Range batholith and probably not related to calc-alkaline rocks of the ba
Tigd
Granodiorite
Medium- to fine-grained, equigranular hornblende-biotite granodiorite plutons, but ranges from granite to quartz monzodiorite (Nelson and others, 1983).  Intrudes Jurassic and Cretaceous rocks of Alaska-Aleutian Range batholith.  Concordant K-Ar ages of
Tign
Gabbronorite
Small, coarse-grained stock of hornblende and biotite-bearing olivine gabbronorite cutting Mesozoic sedimentary rocks (Nelson and others, 1983).  According to Nelson and others, this pluton is most likely related to nearby Tertiary volcanic rocks
TKv
Tertiary and [or] Cretaceous
Volcanic rocks including tuff, tuff breccia, and breccia.  Compositional as well as age data is not available for these rocks (Eakins and others, 1978, W.K. Wallace, written commun., 2002).  Subdivided
TKr
Rhyolite and dacite flows, tuff, dikes, and sills
Rhyolite and dacite flows and tuff cut by dikes or sills which locally contain phenocrysts of sanidine and high temperature quartz.  These rocks primarily occur in the valley of the Mulchatna River in the Lake Clark quadrangle spatially associated with r
TKb
Basalt flows
Scattered occurrences west of Lark Clark.  No further lithologic description available (Eakins and others, 1978).  Thrupp (1987) reported 2 K-Ar dates from this map unit, both whole-rock K-Ar determinations.  One was 44.4 ñ 1.7 and the other 65.8 ñ 13.2
TKg
Granitic rocks, undivided
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink granitic rocks widely present west of the Alaska-Aleutian Range crest.  Chiefly granite, quartz monzonite, and quartz monzodiorite; however, many of the individual plutons include a ran
TKgr
Granite and alaskite
Ranging from very leucocratic alaskite to highly potassic, peralkaline monzogranite, the rocks of this unit are widely distributed in the map area.  In the Dillingham quadrangle (Wilson and others, 2003), a large (7 km in diameter) coarse- to fine-graine
TKgs
Syenitic rocks
Medium-grained biotite monzogranite to syenogranite found in the mountains immediately south of the Koktuli River (Wilson and others, 2003).  Biotite is the only mafic mineral and orthoclase has moderate development of string perthite.  SiO2 of analyzed
TKqm
Quartz monzonite and quartz monzodiorite
Medium- to coarse-grained, light-gray monzogranite or quartz monzodiorite, may contain biotite, hornblende, sodic amphibole, and (or) clino- and orthopyroxene.  Locally contain large phenocrysts of orthoclase; biotite to hornblende ratio is variable but
TKgd
Tertiary and or Cretaceous
Medium-grained, hypidiomorphic granular, seriate granodiorite.  Biotite tends to more abundant than hornblende.  Common in the Lake Clark and Kenai quadrangles (Reed and Lanphere (1972, 1973, Magoon and others, 1976, Detterman and others, 1976).  K-Ar ag
TKqd
Monzodiorite and quartz diorite
Generally located in the central Lake Clark quadrangle and northeast Dillingham quadrangle, these plutons are largely fine- to medium-grained monzodioritic and dioritic rocks, but locally include diorite and gabbro.  Rocks typically have sparse biotite a
Kkg
Kaguyak Formation
Upper Cretaceous, Maestrichtian and Campanian
Consists of a measured thickness of more than 1,200 m of dark-gray to pale-brown, typically thin-bedded, shale, siltstone, and fine-grained sandstone Detterman and others, 1996).  However, only a small area of outcrop occurs within the map area on the so
Ksm
Saddle Mountain section of Magoon and others (1980)
Cretaceous, Maestrichtian
Nonmarine sandstone, conglomerate, and minor siltstone and coal found in the northeast of Chinitna Bay in a section 83 m thick (Magoon and others, 1980).  Consists dominantly of fine- to medium-grained sandstone that fines upward and is generally massive
Kk
Kuskokwim Group, undivided
Cretaceous, Campanian? to Albian?
Sandstone, siltstone, shale, and conglomerate (Cady and others, 1955).  Sandstone is fine- to medium-grained, commonly micaceous gray graywacke or silty graywacke which is occasionally crossbedded, or contains siltstone partings.  Rare argillite pebbles.
Kkn
Kuskokwim Group, nearshore facies
Cretaceous
Sandstone, siltstone, shale, and conglomerate as mapped by J.N. Platt (1957, unpub. data) in the northeastern Taylor Mountains quadrangle.  This informal sub-division of the Kuskokwim Group was originally defined by J.N. Platt (1957, unpub. data).  Mille
Kkv
Kuskokwim Group?, volcanogenic rocks
Cretaceous?
Volcanogenic sedimentary rocks and tuff.  Contains some cherty argillite, minor limestone, and locally, dikes.  Unit defined on the basis of field notes of J.M. Hoare and W.H. Condon (U.S. Geological Survey, 1969 and 1970).  Unit occurs in the northweste
Kg
Plutonic rocks, undivided
No description available beyond granodiorite, quartz diorite, and diorite (Magoon and others, 1976; Reed and others, 1992), but assumed to include representatives of the Cretaceous granitic rocks described below.  Primarily located in the northeast part
Kgd
Granodiorite and quartz monzodiorite bodies mapped by Nelson and others (1983) in the eastern Lake Clark quadrangle, as well as plutons surrounding the Pebble Copper deposit (Bouley and others, 1995) in the Iliamna quadrangle.  The rocks are medium- to c
Kqd
Quartz diorite
Locally foliated, largely medium-grained hornblende-biotite quartz diorite, but includes hornblende-pyroxene gabbro and diorite, quartz diorite, tonalite, and minor granodiorite (Nelson and others, 1983).  Occurs only in the Lake Clark quadrangle.  Reed
Kgr
Coarse-grained, light-pink, biotite granite (Detterman and Reed, 1980, Nelson and others, 1993).  Exposed on the southern margin of the Lake Clark quadrangle and northern Iliamna quadrangle.  No age control available
Kqms
Quartz monzonite and syenite
Late Cretaceous
Massive, coarse-grained light-gray porphyritic quartz monzonite (Detterman and Reed, 1980, Nelson and others, 1993).  Includes plutons in the Iliamna and Lake Clark quadrangles and the pluton of the Okstukuk Hills in the Dillingham quadrangle (Wilson, 19
Klgd
Isolated porphyritic granodiorite body having phenocrysts of quartz, plagioclase, biotite, and glomeroporphyritic clusters of pale-green amphibole in a groundmass of quartz and mostly potassic feldspar in the southcentral Lake Clark quadrangle (Nelson an
KTrag
Togiak-Tikchik Complex - Argillite and graywacke
Lower Cretaceous to Upper Triassic
Gray to gray-green argillite, cherty argillite, graywacke, and minor mudstone, tuffaceous sandstone, and chert.  Unit description is largely derived from the field notes and field maps of J.M. Hoare, W.H. Condon (1969-1970), and W.M. Cady (1943-1944).  T
KTragi
Togiak-Tikchik Complex - Argillite and graywacke, cut by dike swarms
Cretaceous to Triassic
Rocks of map unit KTrag and possibly other map units apparently cut by felsic dike swarms or shallow intrusions.  Host rocks are primarily calcareous argillic graywacke and cherty argillite
KJkr
Koksetna River sequence of Wallace and others (1989)
Lower Cretaceous, Valanginian to Upper Jurassic, Kimmeridgian
Complexly deformed volcanic-lithic turbidites.  Consists of a thick monotonous sequence of thin sandstone (<4 cm) beds interbedded with pelagic shale.  Locally fining upward sequences of sandstone beds reach thicknesses of 1.5 m and have scoured bases an
KJv
Olivine basalt and fragmental volcanic rocks
Cretaceous or Jurassic
Olivine basalt flows and fragmental mafic volcanic rocks.  Apparent range in composition is from andesite to basalt.  Unit is contact metamorphosed by nearby Late Cretaceous and early Tertiary plutonism.  Part of unit KJvs volcanic and sedimentary rocks;
KJvs
Volcanic and sedimentary rocks
Lower Cretaceous to Middle Jurassic
Thick marine unit consisting of low-grade metamorphic or contact metamorphosed volcanic and sedimentary rocks (Hoare and Coonrad, 1978).  This rock unit was mapped by Hoare and Coonrad (1978) in the western Dillingham and adjacent Goodnews Bay quadrangle
KJg
Mafic granitic rocks
Cretaceous and (or) Jurassic
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.  Two samp
Jn
Naknek Formation
Upper Jurassic; Tithonian to Oxfordian
Originally named Naknek Series by Spurr (1900, p. 169-171, 179, 181) for exposures at Naknek Lake on the Alaska Peninsula.  Largely consists of sandstone, conglomerate and siltstone having a primarily plutonic provenance.  This rock unit is widespread in
Jnn
Naknek Formation, Northeast Creek Sandstone Member
Upper Jurassic; Oxfordian
Arkosic sandstone and graywacke.  Called the "lower sandstone member" by Detterman and Hartsock (1966), they considered this unit to have only local significance.  Later work on the Alaska Peninsula (Detterman and others, 1996) showed that the lateral eq
Jnst
Naknek Formation, Snug Harbor Siltstone Member
Upper Jurassic; Kimmeridgian and Oxfordian
Dominantly massive to thin-bedded, dark-gray to black siltstone; calcareous gray sandstone beds are minor part of the unit (Detterman and Hartsock, 1966).  Hard gray limestone concretions and lenses are locally abundant; rare thin layers of volcanic ash
Jnp
Naknek Formation, Pomeroy Arkose Member
Upper Jurassic; Kimmeridgian
Massive light-gray, medium- to coarse-grained arkose containing many interbedded thin beds of dark-gray to brownish siltstone and pebble conglomerate (Detterman and Hartsock, 1966).  The sandstone is rich in quartz (40-45 percent) and sodic feldspar (30-
Jnc
Naknek Formation, Chisik Conglomerate Member
Upper Jurassic
Consists of massive to thick-bedded conglomerate and interbedded, crossbedded, quartzose sandstone.  Clasts, as large as 2 m, are mainly granitic rocks, but up to 20 percent metamorphic and volcanic rocks are present (Detterman and others, 1996).  The un
Jcp
Chinitna Formation, Paveloff Siltstone Member
Middle Jurassic, Callovian
Consists of massive dark-gray arenaceous siltstone in the upper part and a thick sandstone unit at its base (Detterman and Hartsock, 1966).  Large ellipsoidal concretions and lenticular beds of limestone occur throughout the unit and thin interbeds of sa
Jct
Chinitna Formation, Tonnie Siltstone Member
Massive dark-gray to brownish-gray arenaceous siltstone, which weathers brownish-gray to red-brown (Detterman and Hartsock, 1966).  Numerous small yellowish-brown weathering limestone concretions occur in parallel bands and randomly throughout the sectio
Jkw
Graywacke of Kulukak Bay
Middle to Upper Jurassic
A thick marine sedimentary unit consisting of very hard dark-green or gray, massive graywacke and siltstone containing local conglomerate horizons.  Typically consists of sandstone, although coarse pebble conglomerate is locally present.  According to Ho
Jt
Tuxedni Group
Middle Jurassic, Bathonian to Bajocian
Light- to dark-gray and green graywacke, conglomerate, siltstone, and shale (Detterman and Hartsock, 1966).  Graywacke ranges from feldspathic to lithic, conglomerate composed mainly of volcanic clasts in a graywacke matrix.  Unit is locally subdivided i
Jtb
Tuxedni Group, Bowser Formation
Middle Jurassic, Callovian and Bathonian
Heterogeneous assemblage of sandstone, conglomerate, shale and siltstone characterized by rapid facies changes (Detterman and Hartsock, 1966).  Massive light- to dark-gray sandstone and conglomerate are the dominant lithologic types on the Iniskin Penins
Jtt
Tuxedni Group, Twist Creek Siltstone
Middle Jurassic, Bajocian
Soft, poorly consolidated, thin-bedded to massive siltstone and silty shale as much 125 m thick (Detterman and Hartsock, 1966).  The siltstone is dark-gray, weathering to dark-rusty brown and contains many thin beds of volcanic ash that weather a bright
Jtc
Tuxedni Group, Cynthia Falls Sandstone
Middle Jurassic, Bajocian?
Massive to thick-bedded graywacke sandstone and pebble conglomerate about 200 m thick (Detterman and Hartsock, 1966).  The sandstone is medium- to coarse-grained, greenish-gray to dark-green, weathering mottled light-gray due to zeolites and has graded b
Jtg
Tuxedni Group, Gaikema Sandstone
Middle Jurassic, lower middle Bajocian
Resistant, cliff-forming, massive to thin-bedded graywacke sandstone and cobble conglomerate showing graded bedding 150- to 260 m thick (Detterman and Hartsock, 1966).  Conglomerate is confined to the Iniskin Peninsula, clasts in it consist of "red and g
Jtrg
Tuxedni Group, Red Glacier Formation
Middle Jurassic, lower Bajocian to lower middle Bajocian
Thin-bedded to massive, red-brown weathering dark-gray to moderate olive-gray siltstone is concentrated in the upper part of the unit and makes up about 40 percent of the Formation (Detterman and Hartsock, 1966).  The siltstone is highly arenaceous and l
Jms
Togiak-Tikchik Complex - Sedimentary rocks
Lower Jurassic
Marine unit of micaceous, fine-grained black graywacke, siltstone, and slate, and gritty limestone.  Contains Weyla pelecypods of Early Jurassic age.  Cropping out along the Allen River area near where it drains into Lake Chauekuktuli, these rocks occur
Jtk
Talkeetna Formation, undivided
Bedded volcanic rocks widely distributed in the Iliamna, Lake Clark and Kenai quadrangles.  Where undivided, it consists of flows, breccia, tuff, and agglomerate and minor sandstone and shale, often somewhat altered or metamorphosed  (Detterman and Harts
Jtkh
Talkeetna Formation, Horn Mountain Tuff Member
Bedded tuff and tuffaceous feldspathic sandstone, locally containing porphyritic andesite flows.  Bedded tuff occurs in thin-bedded to massive beds that are fine- to coarse-grained, and tan, red, green, purple, or mottled (Detterman and Hartsock, 1966).
Jtkp
Talkeetna Formation, Portage Creek Agglomerate Member
Reddish fragmental volcanic debris, primarily rounded volcanic bomb-like fragments and lapilli tuff (Detterman and Hartsock, 1966).  In contrast to the Marsh Creek Breccia Member, this unit grades to fine-grained tuff, clastic sedimentary rocks and flows
Jtkm
Talkeetna Formation, Marsh Creek Breccia Member
Massive dark-green to green volcanic breccia having a tuff matrix (Detterman and Hartsock, 1966).  Consists of angular fragments of aphanitic pink and green volcanic rocks ranging in size from 1 cm to nearly 1 m.  Interbedded flows of andesite and basalt
JTrp
Togiak-Tikchik Complex - Phyllite and chert
Lower Jurassic and Upper Triassic?
Gray to black cherty phyllitic shale, highly contorted thin-bedded siliceous argillite and local cherty dark calcareous phyllite outcropping along the western margin of the Taylor Mountains quadrangle in association with greenstone of map unit MDv.  The
Jtr
Alaska-Aleutian Range batholith, Trondhjemite
Late Jurassic
Medium- to coarse-grained, seriate, leucocratic trondhjemite containing 10 percent muscovite and about 5 percent interstitial, perthitic potassium feldspar.  This is a large body in the central part of the batholith west of Chinitna Bay.  A single K-Ar a
Jqm
Alaska-Aleutian Range batholith, Granodiorite and quartz monzonite
Jurassic
Whitish-gray, medium-grained, biotite granodiorite, minor hornblende and accessory  primary muscovite.  Medium-grained, light-gray with a pinkish cast quartz monzonite, locally may include quartz diorite and trondhjemite.  This unit is largely exposed on
Jqd
Alaska-Aleutian Range batholith, Quartz diorite, tonalite, and diorite
Medium-grained quartz diorite and tonalite, which are locally foliated.  This is by far the dominant map unit of the Alaska-Aleutian Range batholith.  Hornblende is the dominant mafic mineral, biotite increases in proportion to the presence of quartz and
Jla
Alaska-Aleutian Range batholith, Lamprophyre and basalt dikes
Shown only locally in the join area between the Iliamna and Kenai quadrangles (Detterman and Hartsock, 1966) these dikes intrude map unit Jqd
Mzmi
Mafic igneous rocks
Mesozoic?
Predominantly diabase, probably intrusive.  Isolated outcrops in the north-central Dillingham quadrangle.  Intrudes rocks provisionally assigned to map unit KTrag, suggesting age may be Triassic or younger.  Volcanic rock outcrops to the northeast within
Jmu
Alaska-Aleutian Range batholith, Mafic and ultramafic plutonic rocks
Early Jurassic
Small areas of gabbro, hornblende gabbro, hornblendite, and pyroxenite in the Jurassic batholith Detterman and Reed (1980).  K-Ar ages of 160 and 183 Ma reported (Reed and Lanphere, 1972)
Jssc
Chert, sandstone, and siltstone
Medium-gray to yellowish-gray weathering, medium to thick-bedded, dominantly chert and sandstone unit with locally abundant phosphatic nodules developed in more cherty phases (R.B. Blodgett, 2005, unpub. data).  These rocks are exposed along the peripher
Trcg
Togiak-Tikchik Complex - Triassic limestone
Triassic
Marine unit consisting of chert, tuffaceous cherty rocks, argillite, siltstone, volcanic wacke, conglomerate, limestone, and mafic flows and breccias.  Limestone is generally white to cream colored and recrystallized, however locally it is dark gray and
Trlc
Limestone, silty limestone, and chert
Upper Triassic - Norian
Cream colored to dark-gray, limestone, silty limestone and chert.  Divisible into two subunits: (1) a lower  subunit of massive- to thick-bedded, light-gray to cream colored limestone with common scleractinian corals, spongiomorphs, and lesser brachiopod
Trk
Kamishak Formation, undivided
Upper Triassic; Norian
Limestone, chert, porcellanite, and minor tuff divided into three formal members, in descending order, the Ursus, Middle, and Bruin Limestone Members by Detterman and Reed (1980).  Originally named the Kamishak Chert by Martin and Katz (1912) and renamed
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
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
Trkb
Kamishak Formation, Bruin 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
Trsh
Gray shale and gray volcaniclastic sandstone
Upper Triassic
Gray shale and gray volcaniclastic sandstone.  Unit shown by Eakins and others (1978) in central Lake Clark quadrangle in close proximity to outcrops of the Chilikadrotna Greenstone.  Originally thought to be of Silurian age on the basis of an erroneous
Trv
Togiak-Tikchik Complex - Volcanic rocks
Volcanic rocks comprising at least 5 separate flows, locally as much as 200 feet think interbedded with cherty siltstone.  Associated with sparsely distributed Triassic limestone in the Cinnabar Creek area which yielded  Monotis and Halobia fossils of La
Trc
Cottonwood Bay Greenstone and Chilikradrotna Greenstone
Largely dark-gray to dark-green porphyritic to amygdaloidal basaltic flows altered to greenstone (Detterman and Reed, 1980; Nelson and others, 1983; Wallace and others, 1989).  Locally includes andesite, chert, limestone, and tuffaceous sedimentary rock,
Mzm
Togiak-Tikchik Complex - Melange
Located in the southwest Taylor Mountains and northwest Dillingham quadrangles, this unit consists of two or more rock types in close proximity, typically tightly folded, sheared, and/or altered, including pillowed and massive basalt, chert, gabbro, gray
MzPzu
Metamorphic rocks, undivided
Mesozoic and (or) Paleozoic
Biotite-feldspar-quartz schist, locally actinolite-feldspar-quartz schist or garnet-feldspar-quartz schist (Eakins and others, 1978).  Unit occurs west of Lake Clark
JPk
Kakhonak and Tlikakila Complexes
Jurassic, Triassic, and Permian(?) or older(?)
The Kakhonak Complex, defined by Detterman and Reed (1980), and the Tlikakila Complex, defined by Carlson and Wallace (1983), are lithologically diverse and complex assemblages of metamorphosed mafic plutonic, volcanic, and sedimentary rocks.  Detterman
MzPzb
Metamorphosed mafic volcanic and sedimentary rocks
Metamorphosed mafic volcanic rocks, phyllite, schist, quartzite, marble, calc-silicate rocks, serpentinite, gabbro, and chert (Nelson and others, 1983).  Mixed unit of varying affinity, protolith, and metamorphic age.  Dominant rock type of unit is metam
Pzc
Togiak-Tikchik Complex - Black chert
lower Paleozoic?
Predominantly black and gray chert, but also includes rare white, buff, red, or green bedded to massive chert.  Occasionally vitreous, banded, or fractured.  Interbedded or structurally interleaved with minor amounts of limestone, amygdaloidal basalt, an
Pls
Togiak-Tikchik Complex - Limestone
Permian
Lenses of thin-bedded to massive, light- to dark-gray limestone either interbedded or intercalated with clastic and volcanic rocks in the vicinity of the Tikchik and Wood River lakes.  Locally is gritty conglomeratic, contains siliceous interbeds, or has
Pcs
Togiak-Tikchik Complex - Clastic rocks
Permian?
Fine to coarse-grained, locally 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 contact metamorphosed in some a
Pv
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
TrPzrc
Togiak-Tikchik Complex - Rainbow chert
Triassic? to Paleozoic?
Mostly highly deformed white, gray, red, minor green, or black, thin-bedded to massive, chert.  Locally banded or brecciated and interbedded with minor red siliceous shale, argillite, dolomitic limestone, graywacke, and rare red volcanic rocks and agglom
MDv
Togiak-Tikchik Complex - Greenstone and schist
Mississippian? and (or) Devonian?
Fine- to coarse-grained, massive green to purple altered greenstone, occasionally calcareous or schistose, rarely interbedded with green chert, argillite, and tuff.  Greenschist with occasional chert boudins is a minor part of unit as is shale-chip agglo
Sab
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), algal boundstone
Upper Silurian, Ludlovian and Pridolian
Thick to massive bedded, light gray algal boundstone, locally dolomitized; composed primarily of spongiostromate algal heads (including abundant oncoid forms).  Rock unit represents a barrier reef complex on the outer or seaward margin of the Silurian ca
Sls
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), lime mudstone
Upper Silurian, late Llandoverian to Wenlockian
Primarily thin- to medium-bedded, laminated, dark gray to dark brown, platy lime mudstone, having strong petroliferous odor (Blodgett and Wilson, 2001).  Coarse-grained limestone debris-flows having clasts of algal boundstone reef material common in uppe
Olss
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), tcherskidium-bearing limestone
Upper Ordovician, Ashgillian
Brown, medium- to thick-bedded skeletal lime packstone to wackestone (Blodgett and Wilson, 2001).  Contains abundant pentameroid brachiopods (Tcherskidium,  Proconchidium (or Eoconchidium), and new genus (smooth) aff. Tcherskidium)
Os
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), shale
Ordovician
Extremely poorly exposed brown and dark gray 'chippy' shale, silty shale and minor silicified limestone (Blodgett and Wilson, 2001).  Outcrops in Taylor Mountains D-1 1:63,360-scale quadrangle consist only of frost-boil exposures, however, one rubble out
Oab
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), algal boundstone and lime mudstone
Lower Ordovician
Medium- to thick-bedded, dark-gray to brown algal thrombolites (boundstone) interbedded with light-gray weathering thin- to medium-bedded lime mudstone (Blodgett and Wilson, 2001).  Trilobites and a conodonts (identified by N.M. Savage, written commun. 1
Ols
Thin- to medium-bedded, yellow-gray weathering, dark-gray fresh, burrow mottled lime mudstone (Blodgett and Wilson, 2001).  Peloidal mudstone locally common.  Age control based on poorly preserved low-spired gastropods and conodonts including Drepanoisto
Cls
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), llimestone
Middle Cambrian
Two separate Middle Cambrian limestone subunits are included in this unit in the adjoining Sleetmute A-2 1:63,360 scale quadrangle where it is best developed and exposed (Blodgett and others, in prep).  The upper and thicker overlying subunit, exposed in
Cs
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), clastic and carbonate rocks
Lower Cambrian
This unit is quite heterogeneous and consists of dark-gray (weathering light-gray) orthoquartzite, locally having well-developed parallel laminations; light-gray (weathering white), thin- to medium-bedded lime mudstone having abundant trilobites (observe
DZn
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), undivided
Devonian(?) to Proterozoic
The map units described here come largely from the unpublished work of R.B. Blodgett and co-workers
Zs
Farewell terrane, Nixon Fork subterrane of Decker and others (1994), dolostone, limestone, orthoquartzite, and minor chert
Neoproterozoic?
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