nm
Not mapped
Areas not mapped on Saint Matthew and Hall Islands
ST002
Saint Matthew
Q
Surficial deposits
Quaternary
Undifferentiated beach, bar, alluvial, and colluvial deposits.  Mostly gravel and sand
Unconsolidated
Qu
Undifferentiated fluvial and marine gravel, sand, silt, and mud; organic materials; eolian sand and silt; and colluvium.
BI002
Baird Inlet
NI002
Nunivak Island
KB002
Kuskokwim Bay
Qa
Alluvium
Holocene and Pleistocene
Unconsolidated alluvial, colluvial, glacial outwash, lacustrine, and eolian conglomerate, sand, silt, and mudrock
BH002
Bethel
Unconsolidated deposits
Holocene
NI003
CM003
Cape Mendenhall
KB003
Surficial deposits, undivided
Quaternary?
Areas on map not assigned to bedrock geologic units, assumed to be surficial deposits.  Not described.
GO005
Goodnews Bay
HG003
Hagemeister Island
NG006
Nushagak Bay
Qc
Colluvium
Chiefly frost-rived rubble, loccally includes stream alluvium, terrace gravels, glacial deposits, and windblown silt
HG005
Qs
NG007
Chiefly frost-rived rubble, locally includes stream alluvium, terrace gravels, glacial deposits, and windblown silt
GO008
GO006
Chiefly frost-rived rubble, but locally includes small amount of bog deposit, flood-plain alluvium, terrace deposit, glacial gravel, and wind-blown silt.
BH004
Tidal flat deposits
Quaternary, Holocene
Undifferentiated fluvial and marine gravel, sand, silt, and mud; organic materials
BI001
KB001
Qtf
Tidal flats
NG001
HG001
GO001
Alluvial deposits
Flood-plain alluvium (sand, gravel, and boulders), beach (sand and small pebbles) and estuarine deposits (clay rich silt), and dunes (fine-grained sand).
GO002
HG002
Qal
NG002
Qf
Flood plain alluvium
Alluvium, includes some beach deposits
Flood-plain alluvium
Mud, silt, sand, gravel, boulders, and intermixed wood, peat, and other vegetal material.
Alluvial ssand, gravel, and silt along major streams and rivers.    Deposits are locally transitional to undivided surficial deposits, estuarine and tidal flats deposits.  Locally older alluvium may constitute the material of marine terraces
BI003
Qrs
Reworked silt deposits
Silt, sandy silt, and bog deposits
Reworked silt
Chiefly reworked silt, sandy silt, and bog deposits underlying a plain transitional with or slightly above areas of flood-plain alluvium of Recent age and separated from higher plains and residual 'islands' of older silt deposits by an erosional scrap 10
Derived by extension from adjacent Goodnews Bay quadrangle map.  Chiefly reworked silt, sandy silt, and bog deposits underlying a plain transitional with or slightly above areas of flood-plain alluvium of Recent age and separated from higher plains and r
Qb
Beach deposits
Older beach deposits
Older raised beach ridges on mainland along Kuskokwim Bay.  Derived from interpretation of topographic maps and Google Earth image.  Deposits are locally transitional to undivided surficial deposits, alluvial deposits, and locally may constitute the mate
NI004
Qes
Raised estuarine deposits
Qmt
Underlain be older estuarine and alluvial deposits
Marine terrace
Raised surface underlain by a varity of unconsolidated deposits, especially including older beach, estuarine, alluvial, and probably glacial deposits
Older raised beach ridges eroded to constitute raised marine terraces on mainland along Kuskokwim Bay.  Derived from interpretation of topographic maps and Google Earth image.  Deposits are locally transitional to undivided surficial deposits, alluvial d
Late alluvial sediments, mostly sand, St. Paul Island
Late alluvial sediments, mostly sand.  In most places, the sand is loose and moves with the wind.  Along the north shore of St. Paul Island, impressive dunes are formed
PI002
Pribilof Islands
Qd
Eolian deposits
Dunes (fine-grained sand).
Silt deposits
Light- to dark-gray silt and sandy silt
Qsd
Inferred by extrapolation from adjacent Bethel and Goodnews Bay quadrangles.  Chiefly light- to dark-gray silt and sandy silt containing abundant permafrost.  Deposits become sandier with depth and locally contain pebbles and wood fragments.  Deposits ar
Organic muck containing mammoth remains and nonmarine gastropods occur locally near top of deposits
Chiefly light- to dark-gray silt and sandy silt containing abundant permafrost.  Deposits become sandier with depth and locally contain pebbles and wood fragments.  Deposits are probably of nonmarine fluvial origin but may include eolian and marine membe
Qg
Glacial Deposits
Glacial drift deposited during the last three glacial advances.  Sand, gravel, and boulders.  Includes moraines.  Also includes colluvium, talus, landslide debris, alluvium, and local silt.
Glacial drift deposited during the last three glacial advances.  Sand, gravel, and boulders.  Includes moraines.  Also includes colluvium, tallus, landslide debris, alluvium, and local silt.
Qt
Glacial till
Pleistocene
Unconsolidated glacial till; ground lateral and end moraines
Glacial drift
Poorly to well-sorted silt, sand, gravel, and boulders; stipple indicates well-defined end and lateral moraines
Poorly to well-sorted silt, sand, gravel, and boulders
Chiefly unsorted and poorly sorted sand, gravel, and boulders comprising various types of ice-contact and glaciofluviatile deposits; small areas of glacial outwash, colluvium, and alluvium included with unit.
Qm
Morainal ridges
Morainal ridges of all ages; however most are probably associated with Late Wisconsin events.  Topographic map interpretation enhanced by data from Warren Coonrad
Qo
Outwash deposits
Most probably associated with Late Wisconsin events
Poorly to well-sorted silt, gravel, and boulders in terraces and outwash fan-plains
Poorly to well-sorted sand and gravel with some silt and a few boulders, constituting terraces and outwash-fan plains.
QTs
Semiconsolidated marine beach deposits
Pleistocene or Pliocene
Semiconsolidated marine beach deposits.  Poorly bedded, soft, pebbly siltstones cap volcanic rock sea cliffs.
shallow marine fossils of Plio-Pleistocene age
Sedimentary
Pyroclastic deposits, St. Paul Island
Pyroclastic deposits, largely basaltic tuff
Igneous
Pyroclastic deposits, Otter Island
Pyroclastic deposits
Tuff, St. George Island
Tuff
Pyroclastic deposits, St. George Island
Pleistocene sediments, some fossiliferous, St. Paul Island
Pleistocene sediments, some fossiliferous.  Polymictic, but composed primarily of basaltic boulders and clasts.  Locally cross-bedded
Fossiliferous sediments, St. George Island
Fossiliferous sediments consisting of sand and yellow tuff containing rounded basalt pebbles.  Sediemts overlie a glaciated surface of the peridotite upon which Pleistocene fossil shells have been cemented. The sediments are quite varied; however, a basa
Pelecypods and gastropods of Pleistocene age
Sedimentary deposits, Otter Island
Sediments
Qkn1
Alkalic basalt of Karon Lake
Pleistocene and Holocene
Alkalic basalt of Karon Lake; cinder cones, flows, and tephra; normally polarized rocks of Brunhes polarity epoch
Qtb
Basalt of Togiak River Valley
Fine- and medium-grained, columnar jointed tholeiite and alkali-olivine basalt flows on the floor of the broad Togiak River Valley.
K/Ar age of 0.758 +/- 0.2 m.y.
Fine- and medium-grained, columnar jointed tholeiite and alkali-olivine basaltflows on the floor of the broad Togiak River Valley.
Qmn1
Tholeiitic basalt of Mekoryuk
Tholeiitic basalt of Mekoryuk; massive, columnar-jointed flows; normally polarized rocks of Brunhes polarity epoch
Basalt
Unaltered olivine tholeiite basalt flows having diktytaxitic texture.  Contains olivine, subophitic clinopyroxene, plagioclase and iron oxides with sparse interstitial volcanic glass.
Whole rock K/Ar age of 0.418+0.016 Ma
Quaternary basalt (Togiak basalt of Hoare and Coonrad, 1980)
Subaerial alkali olivine basalt flows, columnar, jointed with ropy tops; includes minor interflow tuffs and breccias. Generally nonporphyritic, dark-gray to black rock with fine microcrysts of labradorite, augite, olivine, and accessory magnetite, with d
Whole-rock K-Ar determination on lower unit yields 0.78 +/- 0.2 m.y.
QTb
Quaternary or Tertiary (early Pleistocene or late Pliocene
Highly vesicular and scoriaceous black olivine basalt flows showing little or no alteration; matrix chiefly volcanic glass.
Qmr1
Tholeiitic basalt of Mekoryuk; massive, columnar-jointed flows; reversely polarized rocks of Matuyama polarity epoch
Qmn2
Tholeiitic basalt of Mekoryuk; massive, columnar-jointed flows; normally polarized rocks of Matuyama polarity epoch
Qmn3
Basaltic flows, St. Paul Island
Basaltic flows and sills.  Flows range in thickness from 20 cm to 7 m or more.  Some are vesicular, some dense.  Compositionally they are basalt and olivine hylobasanite, alkalic
Basaltic flows, St. George Island
Basaltic flows and sills.  Flows range in thickness from 20 cm to 7 m or more.  Some are vesicular, some dense.  Compositionally they are basalt and olivine basanite, alkalic
Hylobasanitic flows, Otter Island
Lava flows of hylobasanite at leaat 325 feet thick, alkalic
QTv
Mafic volcanic rocks
Quaternary/Tertiary
Basalt lava flows and cinder cones.
CM002
Qkr1
Alkalic basalt of Karon Lake; cinder cones, flows, and tephra; reversely polarized rocks of Matuyama (?) polarity epoch
Qkn2
Alkalic basalt of Karon Lake; cinder cones, flows, and tephra; normally polarized rocks of Matuyama (?) polarity epoch
Ta
Alkalic basalt of Ahzwiryuk Bluff
Tertiary, Pliocene
Alkalic basalt of Ahzwiryuk Bluff; nubbly mottled flows and pyroclastic ejecta; includes both normally and reversely polarized rocks older than Gauss polarity epoch
Tbn1
Tholeittic basalt of Binakslit Bluff
Tholeittic basalt of Binakslit Bluff; massive, columnar-jointed flows; normally polarized flows of Gauss polarity epoch
Tb
Tholeittic basalt of Binakslit Bluff; massive, columnar-jointed flows; includes both normally and reversely polarized flows older than Gauss polarity epoch
Tif
Felsic intrusive rocks
Tertiary
Light-colored, fine-grained, commonly porphyritic felsic intrusive rocks.  Chiefly rhyolitic to dacitic dikes and sills
K/Ar age of 13 +/- 0.5 m.y. from biotite.
Tr
Tertiary rhyolite
Abundant sills and dikes cutting Kus and Jln in vicinity of Nunavarchak Lake (only largest body shown). Consists of cream-colored, often iron-stained, aphanitic to porphyritic rhyolite to dacite. Phenocrysts are quartz, plagioclase, orthoclase, and acces
Yields a K-Ar biotite age of 13.0 +/- 0.5 m.y.; however, its association with feeder dikes of Upper Cretaceous volcanic rocks suggest true intrusive age may be Late Cretaceous.
Tnr
Nukluk Volcanic Field; rhyolite
Tertiary, Eocene
Moderately altered rhyolite flows, domes, and ash-flow tuffs.  Rhyolite of the main volcanic field contains phenocrysts of sanidine, riebeckitic amphibole, and rare quartz.
Ar/Ar total-fusion age of 54.7+1.6 Ma from riebeckite
Tnba
Nukluk Volcanic Field; basalt and andesite
Massive, columnar-jointed, basalt and subordinate andesite flows.  Minor latite and dacite.  Overlies Tnr in Fog River area.  Elsewhere, interbedded.
Rhyolite and dacite tuff
Chiefly rhyolite and dacite welded tuff and tuff breccia and dark rhyolite vitrophyre in the northern part of map area.  Chiefly light-colored rhyolite and dacite hypabyssal rocks in the southern part of the map area.  May be extrusive and hypabyssal cog
Aplite, St. George Island
Aplite granite dike intruding peridotite.  Surface weathered before eruption of overlying basatic flows
TKst
Swift Creek Volcanic Field; Rhyolite ash-flow tuff
Early Tertiary and (or) Late Cretaceous
Fresh to moderately altered, densely welded rhyolite ash-flow tuff.  Chiefly black glassy vitrophyre.
TKsr
Swift Creek Volcanic Field; Rhyolite
Frost-riven rubble from single rhyolite dome(?)
TKer
Eek Volcanic Field; Rhyolite
Paleocene and Cretaceous (?)
Pale pink to orange rhyolite domes found as small knobs or large domical hills as large as 4 km in diameter with 300 to 500 m in relief.
Whole rock K/Ar age of 62.5+1.9 Ma and 59.3+1.8 Ma
TKtb
Tulip Volcanic Field; Block and ash flow
One block and ash flow mapped in area.  Broken blocks of dacite in an ashy matrix of the same lithology.  Interpreted as a hot avalanche deposit formed during dome collapse.  Dacite contains very coarse (up to 14 mm) phenocrysts.
Albite rhyolite
Tertiary(?)
Light- to medium-gray, fine-grained, porphyritic albite rhyolite, commonly shows well-developed flow structures.  Forms small stock-like bodies, dikes, and sills.
TKtd
Tulip Volcanic Field; Dacite and Andesite flows and Dacite tuff
Dacite and subordinate andesite flows and underlying dacite pyroclastic rocks.  Flows crop out as columnar-jointed cliffs.
TKsa
Swift Creek Volcanic Field; Andesite flows
Columnar-jointed andesite flows capping small hills that overlie unit Ksl.
TKea
Eek Volcanic Field; Andesite flows and Porphyry
Small outcrops and columnar jointed andesite flows.  Subordinate altered andesite porphyry.  Minor basalt, andesite lithic tuff, and dacite.
Ar/Ar total-fusion age of 59.5+12.3 Ma from plagioclase
Tv
Volcanic rocks
middle to late Tertiary
Chiefly black, porphyritic olivine basalt; includes some andesitic flows and water-laid tuff and a small amount of obsidian and siliceous tuff.  Rocks are moderately folded and unconformable on steeply dipping rocks of Cretaceous age and older.
Tf
Felsic rocks
Pink and gray, fine-grained quartz-feldspar porphyry; locally shows flow structure.  Possibly a felsic border facies of granitic rocks similar to felsic rocks associated with the Horn Mountain stock in the central Kuskokwim region (Cady, 1955).
Peridotite, St. George Island
Peridotite, forms basement of island.  Massive, originally was a dunite and now largely altered to serpentine and magnetite.  The upper surface of the peridotite is an erosion surface, shows glacial striae, appears polished, and has a brownish-black varn
TKg
Granitic rocks
Tertiary and Cretaceous
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
Kug
Upper Cretaceous granitic plutons
Late Cretaceous
Medium-grained granitic plutonic rocks, ranging from quartz monzonite to granodiorite to diorite, with accessory biotite and (or) hornblende (Hoare and Coonrad, 1978a). Intrude a variety of units across map, with narrow biotite-hornblende hornfels zones.
Age based on several K-Ar determinations.
TKif
Fisher Dome and Marvel Creek plutons, undivided
Small intrusions of about 1 km (square).  Hornblende-biotite granite and granodiorite porphyry.  Randomly oriented euhedral brown hornblende, brown biotite, plagioclase, and resorbed quartz phenocrysts in a fine-grained aplitic matrix of quartz, plagiocl
Tg
Pink, light- to dark-gray, fine- to coarse-grained granite, quartz monzonite, granodiorite, and diorite.
Tn
Igneous rocks of Nayorurun River area
Intrusive-extrusive complex consisting of dikes, sills, and related tuffs and breccias in the Nayorurun River area.
K/Ar age of 60.7 +/- 1.8 m.y. from biotite
Tial
Aniak Lake pluton
Tertiary, Paleocene
Coarse-grained, porphyritic to seriate leucocratic biotite granite pluton 10 km (square) in area.  Speckled texture with randomly oriented feldspar phenocrysts.  Porphyritic rhyolite dikes common in the uppermost part of pluton and in surrounding biotite
Ar/Ar total-fusion age of 60.8+1.8 Ma from biotite
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.  Subdivision of granite from original Hoare and Coonrad (1978) unit.
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite
TKik
Quartz monzonite of Kipchuk River
Small (< 1 km (square)) quartz monzodiorite intrusion in Kkcd of Kuskokwim Group causing contact metamorphism of Kkcd.  Medium-grained, intergranular-textured biotite-augite quartz monzodiorite and quartz diorite.
Kick
Crooked Mountain pluton
Large composite pluton with thin gabbro and diorite margin that partially rims and is intruded by massive core of biotite-hornblende granodiorite and granite.  Dominantly augite-biotite-hornblende and (augite-) hornblende-biotite granodiorite, quartz mon
Ar/Ar total-fusion age of 69.8+2.1 Ma from biotite
Kicc
Canyon Creek pluton
Small (~1 km (square)), medium- to coarse-grained, intergranular to hypidiomorphic granular augite-biotite quartz diorite to hornblende-biotite granodiorite.
Ar/Ar total-fusion age of 70.3+2.1 Ma from biotite
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.  Subdivision of quartz monzonite from original Hoare and Coonrad (1978) unit.
Granodiorite
Fine-grained hornblende granodiorite
K/Ar age of 62.2 +/- 2 Ma (recalc) from hornblende
Ticp
Cripple Mountain pluton
Paleocene
Elliptical, erosionally recessive pluton, 40 km (square).  Coarse-grained, hypidiomorphic-granular hornblende-biotite granodiorite and granite, with lesser quartz monzodiorite and quartz monzonite.  Aplite dikes near pluton margin.
Ar/Ar total-fusion age of 62.2+1.9 Ma from biotite
TKin
North Fork pluton
Two phases:  Main Felsic Phase is seriate to hypidiomorphic granular (augite-) hornblende-biotite quartz monzodiorite, granodiorite, and minor biotite granite.  Aplite dikes are common.  Mafic Phase is a coarse-grained cumulus-textured augite quartz gabb
Ar/Ar total-fusion age of 64.3+1.9 Ma from biotite in Felsic Phase.
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.  Subdivision of tonalite-monzonite from original Hoare and Coonrad (1978) unit.
TKie
Eek River pluton and related plutonic rocks
Sill 50 to 500 m thick crops out in discontinuous exposures over 10 km length cutting and contact-metamorphosing Kkcd of Kuskokwim Group north of Eek River.  Dominantly medium- to coarse-grained, porphyritic to diabasic (hornblende) augite diorite, quart
TKig
Gemuk Mountain pluton
Elongate, north-trending, erosionally resistant, mafic to intermediate quartz gabbro to mafic granodiorite pluton, 25 km (square).  Cuts and contact-metamorphoses units Kkv of Kuskokwim Group and Kvs of Togiak Terrane.
TKip
Mt. Plummer pluton
Medium- to coarse-grained, erosionally resistant, hypidiomorphic granular augite-biotite mafic granodiorite, quartz monzodiorite, and quartz diorite pluton.  Intrudes and contact metamorphoses Kkmf, Kksh, and Kkcd of Kuskokwim group.
K/Ar ages of 65.5+2.0 Ma and 66.6+2.0 Ma from biotite
Kihd
Hornblende diorite stocks and dikes
Small, extensively altered, hornblende diorite stocks and dikes containing relict euhedral plagioclase.
Ar/Ar total-fusion age of 68.0+2.0 Ma from hornblende
Fine-, medium-, and coarse-grained, light- to dark-gray, rarely pink plutonic granitic rocks.  Chiefly quartz monzonite, granodiorite, and quartz diorite.  Subdivision of quartz diorite and diorite from original Hoare and Coonrad (1978) unit.
Tim
Mafic intrusive rocks
Dark-colored dikes and sills consisting of diabase, basalt, dioritic and gabbroic mafic intrusive rocks.
K/Ar age of 64.6 +/- 2 m.y. from biotite
Dark-colored dikes and sills consisting of diabase, basalt, dioritic and gabbroic mafic intrusive rocks
Gabbro
Medium- to coarse-grained pyroxene gabbro dike (?)
Tm
Mafic rocks
Gabbro, diabase, basalt, and biotite lamphrophyre in stocks, sills, and dikes.
Ks
Sedimentary rocks of Summit Island
Late Cretaceous (Maestrichtian (?))
Sedimentary rocks of Summit Island.  A sequence of intertonguing nonmarine conglomerate, sandstone, shale, and carbonaceous mudstone containing abundant plant detritus and a few coal seams.
Palynomorphs indicate Late Cretaceous
Kus
Upper Cretaceous nonmarine clastic rocks (Summit Island Formation of Hoare and others, 1983)
Nonmarine clastic rocks, moderately to well indurated, including (in order of abundance) black carbonaceous shale, fine to coarse sandstone, conglomerate, and thin coal seams. probable depositional contact on deformed older rocks not exposed. Divisible i
Fossils pollen suggest a Late Cretaceous, possibly Maestrichtian, age.
Kk
Kuskokwim Group
Cretaceous
Kuskokwim Group.  Marine sedimentary sequence consisting of graywacke, sandstone, conglomerate, siltstone, and shale.
Early Cretaceous (Albian) age assigned from fossils found north of the map area.
Kkcf
Kuskokwim Group; Chert-clast provenance rocks; Outer-fan turbidite facies
Late Cretaceous (Turonian)
Thin-bedded, fine-grained, quartzose sandstone and slate with lesser thin- and thick-bedded medium-grained sandstone.
Age considered Turonian (Late Cretaceous) based on three megafossil collections
Kkmf
Kuskokwim Group; Mixed provenance rocks; Outer-fan turbidite facies
Shale-rich sequence with lesser thin- to thick-bedded, medium-grained sandstone sections.
Age considered Turonian (Late Cretaceous) based on two megafossil occurences
Kkmc
Kuskokwim Group; Mixed provenance rocks; Inner-fan-channel facies
Mixed shale-rich and sandstone-rich sections, with coarse sandstone and pebbly sandstone in thick-bedded, amalgamated sequences with minor interbedded shale.
Recovered fossils are nondiagnostic Cretaceous forms
Kkv
Kuskokwim Group; Volcanic provenance rocks
Interbedded shale, siltstone, sandstone, and conglomerate composed of rounded clasts of volcanic, volcaniclastic, and plutonic rocks.
Age considered Turonian (Late Cretaceous) based on megafossil occurences
Kksh
Kuskokwim Group; Shale and siltstone
Late Cretaceous (Early Turonian and (or) Late Cenomanian)
Dark-gray to black, finely laminated shale, siltstone and thin-bedded, very fine grained sandstone.
Age constrained by megafossil occurances of late Cenomanian and (or) early Turonian age low in section and by overlying units of Turonian age
Kks
Kuskokwim Group, sedimentary rocks
middle Late (Cenomaniam and Coniacian) to late Early Cretaceous (Albian)
Chiefly consist of interbedded graywacke, siltstone, with lesser amounts of pebble grit and conglomerate and a small amount of coal.  Well-indurated, commonly light- to dark-gray and weather brown.  Vary from volcanic wacke to quartz-chert-feldspar-rich
Fossils collected from basal zone are considered late Early Cretaceous (Albian) age and fossils from the upper zone considered early and middle Late Cretaceous (Cenomanian and Coniacian)
KCgg
Gemuk Group, graywacke, siltstone, and conglomerate
Early Cretaceous to Mississippian(?)
Graywacke and conglomerate, massive, fine- to coarse-grained hard, dark-gray; massive and thin-bedded, light- to dark-gray and green lithic-feldspathic graywacke; massive varicolored argillite; banded slaty siltstone; minor amounts of limestone, calcareo
Fossils of early Cretaceous (Valanginian) and Late Jurassic age collected at widely scattered localities.
Kkcd
Kuskokwim Group; Chert-clast provenance rocks; Deltaic facies
Thick bedded quartzose sandstone, pebbly sandstone, and subordinate siltstone and shale.  Re-assigned polygon from Hoare and Coonrad (1978) to subdivide Kuskokwim to match Box and others (1993)
Thick bedded quartzose sandstone, pebbly sandstone, and subordinate siltstone and shale.
Kkbc
Kuskokwim Group; Basal Conglomerate
Late Cretaceous (Cenomanian(?))
Pebble to boulder conglomerate, coarse sandstone, and minor interbedded medium-grained sandstone, siltstone, and shale.
Kuskokwim Group, sedimentary rocks, conglomerate facies
Chiefly consists of conglomerate facies of interbedded graywacke and siltstone, with lesser amounts of pebble grit conglomerate and and a small amount of coal.  Well-indurated, commonly light- to dark-gray and weather brown.  Varies from volcanic wacke t
Fossils collected from basal zone are considered late Early Cretaceous (Albian) age and fossils from the upper zone considered early and middle Late Cretaceous (Cenomaniam and Coniacian)
Graywacke-siltstone sequence
Late Cretaceous(?)
Volcanic graywacke, siltstone, and minor amounts of pebble conglomerate and coal; probably littoral marine.
Ks?
Sedimentary rocks
Kcg
Graywacke and conglomerate
Early Cretaceous
Marine sedimentary unit consisting of hard graywacke, shaly and blocky siltstone, and local conglomerate.  Rocks commonly calcareous.
Buchia of Early Cretaceous (Valanginian age)
Kts
Turbidite sandstone, conglomerate, and phyllite, Goodnews terrane
Sandstone, sandy conglomerate, pebbly mudstone, siltstone, and shale with phyllitic fabric.  Reassigned polygon from Hoare and Coonrad (1978) to match unit from Box and others (1993) to north.
Pelecypod fossil collection of Valanginian, and of Late Jurassic and (or) Early Cretaceous, age
Sandstone, sandy conglomerate, pebbly mudstone, siltstone, and shale with phyllitic fabric.
Kv
Volcanic graywacke and argillite
Thinly interbedded fine-grained graywacke and siliceous argillite thermally altered by granodiorite (Tg)
HFS
Kb
Graywacke of Buchia Ridge
Marine sedimentary rocks of graywacke, siltstone, and conglomerate.  Conglomerate, near the top of Buchia Ridge, contains local Buchia shell coquinas.
Buchia and other "Fossils" show that it is Early Cretaceous in age (Valanginian and Hauterivian ages)
Klb
Lower Cretaceous graywacke of Buchia Ridge
Lithic sandstone, conglomerate, and shale at least 2-5 km thick (Hoare and Coonrad, 1983). Clastic rocks composed mostly of slaty volcaniclastic rock fragments, similar to Jurassic rocks to the southeast (Jln, Jmm). No paleocurrent data available. Divisi
Klb1 preserves abundant Valanginian fauna; Klb2 yields rare Hauterivian ammonites.
Klg
Limy grit and limestone
Limy grit and limestone.  Chiefly small, green, fine-grained angular rock fragments and minor round quartz pebbles cemented by gray bioclastic limestone consisting of tiny shell fragments.  Coeval with the conglomeratic rocks of Buchia Ridge (Kb).
Tuff and sedimentary rocks
Thick, varied assemblage of andesitic, commonly laumontitized, tuffs, sedimentary rocks, and a few flows.
Buchia of Early Cretaceous (Valanginian age)  Radiolaria of Early Cretaceous age
Kvs
Togiak Terrane; Marine volcaniclastic sandstone, conglomerate, shale, and interbedded tuff
Thin- to thick-bedded, green tuffaceous sandstone, siltstone, argillite, conglomerate, tuff, and tuffaceous chert.
Early Cretaceous pelecypods and radiolarians
Early Cretaceous to Late Jurassic
Ktr
Tulip Volcanic Field; Rhyolite domes and flows
Rhyolite domes and flows found as small knobs or hills.  Moderately to severely altered.
Kvkr
Kipchuk Volcanic Field; Rhyolite domes and flows
Moderately to severely altered, white to orange, platy rhyolite domes and flows, and minor rhyolite breccia.  Lithologically similar to Ktr.
ALT
Volcanic rocks and volcanogenic deposits
Early Tertiary
Mostly andesitic and trachytic tuffs, breccias, and flows.  Lesser basaltic andesite and diabase and fine- to medium-grained volcanogenic sediments
TKm
Mafic flows and volcaniclastic deposits
Early Tertiary to Late Cretaceous
Flat-lying to gently dipping mafic flows of andesite and basalt, and volcaniclastic deposits of andesitic and basaltic tuff and conglomerate
K/Ar age of 78.7 +/- 2 and 66.4+/- 2 m.y. from whole rock samples of basalt
Kuv
Upper Cretaceous volcanic rocks
Moderately to steeply dipping, fresh to weakly altered porphyritic andesite flows and interbedded sandy to bouldery volcaniclastic rocks. Phenocrysts are plagioclase, clinopyroxene, orthopyroxene, pseudomorphic talc after olivine, and accessory magnetite
Four whole-rock K-Ar determinations yield Late Cretaceous ages.
Kvk6
Kipchuk Volcanic Field; Andesite and Basalt flows
Late Cretaceous (Maastrichtian)
Porphyritic plagioclase-pyroxene-olivine andesite flows and flow breccias, minor interbedded flows of olivine basalt, and black andesite tuff.
Ar/Ar total-fusion age of 69.5+2.1 Ma from biotite
Kvk3
Kipchuk Volcanic Field; Andesite flows
Porphyritic, propylitically altered, one- and two-pyroxene andesite lava flows.  Minor olivine basalt flows, dacite flows, and andesite tuff.
Kvk1
Kipchuk Volcanic Field; Basal Andesite flows
Light-gray to tan, sugary textured, fine-grained andesite flows with well-developed flow banding and irregular platy fracture.
Ksl
Swift Creek Volcanic Field; Lithic air-fall tuff
Late Cretaceous (Campanian)
Moderately altered, andesitic lithic air-fall tuffs, tuff breccias, and altered andesite flows.  Varies from coarse-grained lithic tuff breccia with clasts as large as 2 m in diameter to ash beds containing lithic fragments less than 0.6 cm in diameter.
Whole rock Ar /Ar total-fusion age of 74.3+2.2 Ma
Kvk5
Kipchuk Volcanic Field; Fine-grained tuff, crystal-vitric tuff, and tuffaceous sandstone
Late Cretaceous (Maestrichtian)
Lacustrine, fluvial, and air-fall tuff.  Very fine- to fine-grained tuffs that are finely laminated.  Air-fall tuff is fine- to medium-grained with well developed bedding.
Kvk4
Kipchuk Volcanic Field; Upper black Andesite lithic tuff
Black, densely welded andesite tuff exposed in low hills and ridges.
Whole rock K/Ar ages of 69.0+2.1 Ma and 71.4+2.1 Ma
Kvk2
Kipchuk Volcanic Field; Lower black Andesite lithic tuff
Massive, dark, fine-grained tuff having black opaque vitroclastic groundmass and abundant lithic fragments of volcanic rocks and lesser sandstone and shale.
Ki
Intermediate and silicic pyroclastic deposits
Intermediate and silicic pyroclastic deposits including: dacite, andesite, and rhyolite nonwelded tuff breccia and crystal tuff, dacite and rhyolite welded tuff, massive dacite breccia (lahar?), fine ash-fall tuff, volcanic conglomerate, and andesite and
Pollen assemblages from carbonaceous tuffs
K/Ar age of 74.1 +/- 2 and 74.4+/- 2 m.y. from biotite and hornblende
Ksp
Serpentinite
Small, pervasively slickensided bodies of serpentinite, serpentinite-matrix melange, and silica-carbonate altered serpentinite.
s
Serpentine
Fibrous pale-green and massive black serpentine forming a small intrusive body north of mouth of Crooked Creek.
Kinc
Nyac, Bonanza Creek, and Columbia Creek plutons, undivided
Rock is pale-pink weathering light-gray, coarse-grained porphyritic to seriate hornblende-biotite and biotite-hornblende granite, quartz monzonite, and lesser granodiorite and quartz-monzodiorite.  Nyac (~200 km) is crudely concentrically zoned from horn
Nyac: K/Ar age of 101.1+3.0 Ma from hornblende; 108.5+3.3 Maÿand 120.0+3.6 Ma from biotite; and U/Pb age of 104 to 129 Ma from zircon.  Bonanza Creek: Ar/Ar total-fusion age of 110+3.3 Ma from biotite.  Columbia Creek: K/Ar age of 115.0+3.5 Ma from bioti
KJc
Togiak Terrane; Argillite and tuffaceous chert
Early Cretaceous and (or) Late Jurassic
Thin-bedded green to brown argillite with occasional 1- to 4-cm thick tuffaceous chert, siltstone, and fine-grained tuff interbeds.
Late Jurassic and (or) Early Cretaceous age from poorly preserved radiolarians
KJba
Basaltic and Andesitic lava flows, Nyac terrane
Basaltic and andesitic lava flows.
KJvs
Volcanic and sedimentary rocks
Early Cretaceous to Middle Jurassic
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, tuffs, and breccias.  Interbedded with the volcanic rocks are tuffaceous siltst
Radiolaria of Late Jurassic to Early Cretaceous age, and fragmentary ammonites of Jurassic age.
BH003
TJih
Hypabyssal felsic intrusive rocks
Early Tertiary (?), Cretaceous, and Jurassic
Highly altered rhyolite and dacite porphyries.
KJb
Togiak Terrane; Pillow basalt
Very altered pillow basalt sequence.   Interbedded with argillite and thin-bedded chert of KJc.
Radiolarian fauna in interbedded KJc
TJis
Slate Creek pluton
Erosionally neutral, medium-grained hypidiomorphic-granular, mafic hornblende tonalite and granodiorite pluton, less than 2 km (square).
Jvs
Togiak Terrane; Marine volcaniclastic sandstone, conglomerate, and argillite
Jurassic
Turbidite-facies volcaniclastic strata, locally as coarse as fine-grained pebble conglomerate
Jvc
Volcaniclastic conglomerate, sandstone, and shale, Nyac terrnae
Late and Middle Jurassic
Epiclastic sequence of tuffaceous marine sandstone, shale, and conglomerate with minor interbedded basaltic and andesitic lava flows
Marine pelecypods of Bajocian age (Middle Jurassic);  Marine pelecypods of Tithonian age (Late Jurassic)
Ja
Togiak Terrane; Marine arkosic sandstone and argillite
Turbidite-facies arkosic sandstone and shale
Jk
Graywacke of Kulukak Bay
Middle to early Late Jurassic
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.
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.  Consists of very hard graywacke and siltstone with local conglomerate.  Locally hornfelsed
Jmm
Middle and Upper Jurassic turbidites of Metervik Bay
Coherently deformed volcaniclastic turbidites southeast of Right Hand Fault. Reconstructed 6 km section, divided into four turbidite facies units (using criteria of Walker and Mutti, 1973): (from bottom to top) a conglomeratic inner fan facies unit; a we
Rare fossils range from Bajocian (base of third unit) to Oxfordian (in upper unit).
Jmm1
Middle and Upper Jurassic turbidites of Metervik Bay, conglomeratic inner fan facies (Unit 1)
Jmm2
Middle and Upper Jurassic turbidites of Metervik Bay, well-bedded outer (or mid?) fan lobe facies (Unit 2)
Jmm3
Middle and Upper Jurassic turbidites of Metervik Bay, massive mid fan channel facies (Unit 3)
Jmm4a
Middle and Upper Jurassic turbidites of Metervik Bay, conglomeratic inner fan facies (Unit 4a, channel margin)
Jmm4b
Middle and Upper Jurassic turbidites of Metervik Bay, conglomeratic inner fan facies (Unit 4b, channel)
Jmm4c
Middle and Upper Jurassic turbidites of Metervik Bay, conglomeratic inner fan facies (Unit 4c, channel margin)
Unit added by extension of polygon from Box (1985).  Description from Box:  Coherently deformed volcaniclastic turbidites southeast of Right Hand Fault. Reconstructed 6 km section, divided into four turbidite facies units (using criteria of Walker and Mu
Jmt
Middle Jurassic volcaniclastic turbidites of Togiak Bay
Middle Jurassic
Tightly folded volcaniclastic turbidites at least 1.7 km thick. Sandstones and conglomerates composed entirely of volcanic and hypabyssal igneous clasts. A few tool marks and interbedded slump folds suggest ENE-directed paleocurrents. Middle Jurassic age
Middle Jurassic age constrained by occurrence of Bajocian pelecypods northeast of map area in Togiak River valley (Hoare and Coonrad, 1978a).
Intruded by Aeolus Mtn. gabbro body with 174 +/- 8 m.y. K-Ar amphibole age.
Jln
Lower Jurassic? dismembered volcaniclastic turbidites
Early Jurassic (?)
Pervasively deformed and dismembered tuffaceous sandstone-shale sequence, predominately argillaceous. Sedimentary structures variably preserved and indicate deposition from turbidity currents and other mass flow processes. Original thickness uncertain. S
Poorly preserved radiolaria from SF1 have been identified as post-Triassic Mesozoic forms. Clasts of slate similar to SF2 occur stratigraphically below Bajocian fossil occurrence in adjacent Middle Jurassic turbidites (Jmm). Deposition and deformation of
Graywacke of Kulukak Bay, subdivided
Subdivsion of unit into Box's (1985) volcaniclastic turbidites.  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.
Jlvs
Early Jurassic
Marine unit of mafic flows, some pillow structure, volcanic breccias, and massive fine- to medium-grained volcanogenic sedimentary rocks.  Fractures commonly coated with laumontite
Weyla pelecypods of Early Jurassic age.
Jlv
Lower Jurassic interbedded volcanic and sedimentary rocks
Basaltic to dacitic volcanic and volcaniclastic rocks. Volcanic rocks (locally pillowed) typically plagioclase +/- clinopyroxene +/- hornblende porphyries. Interbedded with pyroclastic and epiclastic rocks derived from similar volcanic rocks. Grades from
Upper unit of abundantly fossiliferous, well bedded sandstones and shales
TJvb
Upper Triassic-Lower Jurassic coarse volcaniclastic rocks
Early Jurassic-Late Triassic
Dense green tuffs, tuff breccias, pillow breccias, minor pillow basalt, and associated epiclastic rocks. Breccia clasts are aphanitic or plagioclase-clinopyroxene porphyries, often vesicular, mostly angular. Interbedded hyaloclastites and crystal tuffs.
TrJvb
Unit as described by Box (1985), shown as hornfels and unit Jlvs by Hoare and Coonrad (1978).  Dense green tuffs, tuff breccias, pillow breccias, minor pillow basalt, and associated epiclastic rocks. Breccia clasts are aphanitic or plagioclase-clinopyrox
JTrp
Togiak Terrane; Phyllite and chert
Early Jurassic and Late Triassic (?)
Gray, green, and black phyllite, fine-grained tuff, and tuffaceous chert.
Single radiolarian collection of Early Jurassic (?) age
Metamorphic
Jct
Jurassic laminated tuffs and associated rocks
Mixed unit characterized by banded to finely laminated crystal lithic tuffs with interbedded green, white, and black tuffaceous cherts. Minor interbedded sections of massive, coarse-grained lithic tuff and (or) pillow basalt (Jpb). Highly deformed, often
Several cherts have yielded radiolaria of Jurassic age, one of which is identified as Tithonian (latest Jurassic).
Jct (Jpb)
Jpb
Pillow basalt. Highly deformed, often with slaty or spaced cleavage, which is also folded. Partially altered to prennite-pumpellyite facies mineral assemblage. Several cherts have yielded radiolaria of Jurassic age, one of which is identified as Tithonia
Volcanic and sedimentary rocks, subdivided
Jt
Trondhjemite
Jurassic and Jurassic (?)
Light-gray, medium-grained intrusive trondhjemite consisting of abundant quartz, plagioclase, and minor chlorite.
Jg
Gabbroic rocks
Medium- to coarse-grained, locally pegmatitic intrusive gabbroic rocks consisting of hornblende, clinopyroxene, and calcic plagioclase
K/Ar age range of 159.3 to 186.9 m.y. from hornblende
Jmg
Middle Jurassic gabbroic plutons
Medium- to coarse-grained (locally pegmatitic) hornblende gabbro to diorite bodies, slightly altered (i.e., sericitized plagioclase, hornblende partially replaced by actinolite and chlorite, prehnite-quartz veinlets). Intrusive into a variety of units wi
K-Ar amphibole ages range from 186 to 159 (minimum) m.y., or Middle Jurassic.
Volcanic and sedimentary rocks consisting of andesitic, trachytic, and basaltic flows and breccias with interbedded fine- to coarse-grained sedimentary rocks
Fossils in related rocks, north of map area, are assigned a Middle Jurassic age.
Jab
Andesitic and Basaltic lava flows and marine epiclastic rocks, Nyac terrane
Andesitic and basaltic lava flows, flow breccias, and tuffaceous marine sedimentary rocks
Marine pelecypods of Bajocian age (Middle Jurassic)
Kuskokwim Group, volcanic rocks
Massive andesitic and basaltic flows; minor amounts of trachyte, trachyandesite, and dacite; some interbedded tuffaceous sedimentary rocks; and locally several hundred feet of volcanic breccia at or near base.  These rocks from a belt of low rolling hill
Originally called Cretaceous on map; note revised to Jurassic and removed from Kuskokwim.
Kuskokwim Group, volcanic breccia
Several hundred feet of volcanic breccia at or near base of massive andesitic and basaltic flows; minor amounts of trachyte, trachyandesite, and dacite; some interbedded tuffaceous sedimentary rocks.  These rocks from a belt of low rolling hills on the w
Originally called Cretaceous on map; note revised to Jurassic and removes from Kuskokwim.
Jmv
Middle Jurassic interbedded volcanic and sedimentary rocks
Basaltic and andesitic volcanic and volcaniclastic rocks, extensively altered to prehnite-pumpellyite facies assemblage. Volcanic rocks more common in lower third of exposed section, characterized by plagioclase + clinopyroxene +/- hornblende porphyries.
Locally fossiliferous with Middle Jurassic fauna.
Jum
Ultramafic rocks
Serpentinite, serpentinized dunite and websterite ultramafic rocks.
K/Ar age range of 176.4 to 186.9 m.y. from hornblende
Jmu
Middle Jurassic ultramafic plutons
Occur only at Red and Susie Mtns. at west end of map area. Medium-grained dunite, wehrlite, and clinopyroxenite, partially (less than 25 percent) replaced by serpentine minerals. Around margins cut by numerous coarsely pegmatitic hornblendite dikes. Nort
Hornblendite dikes yield Middle Jurassic K-Ar amphibole ages.
Jmf
Middle Jurassic granodiorite pluton
Medium-grained biotite-hornblende granodiorite of Hagemeister Island; slightly altered (i.e. sericitized plagioclase, chlorite partially replacing biotite and hornblende). Intrusive into Lower Jurassic rocks (Jlv) with narrow contact metamorphic zone of
Yielded K-Ar hornblende age of 183 +/- 7 m.y.
Pzmg
Metagabbro and greenstone
Paleozoic (?)
Massive, fine- to coarse-grained, locally pegmatitic, greenish metagabbro and greenstone.  Probable dismembered altered ophiolite complex consisting of mafic flows, dikes, volcaniclastic rocks, and gabbro.
Trub
Upper Triassic (?) pillow basalts
Upper Triassic
Pillow basalts, aphanitic to porphyritic, with interbedded pillow breccia, hyaloclastite, and interpillow and interbedded red and white radiolarian chert. Porphyries consist of plagioclase + clinopyroxene phenocrysts with intergranular to subophitic grou
Considered Upper Triassic based on radiolarian ages of associated bedded chert.
Trut
Upper Triassic (?) trondhjemite
Late Triassic(?)
Altered and irregularly cataclastized trondhjemitic plutonic rocks composed of plagioclase and quartz with minor seams of chlorite, sericite, and clinozoisite (lawsonite locally: Hoare and Coonrad, 1978b). Shown on map only south of Security Cove but sma
Trud
Upper Triassic (?) diabasic intrusive rocks
Subophitic, holocrystalline plagioclase-clinopyroxene diabase (grain size to 1.5 mm). Occurs as 0.3 to 1.0-m-wide sills and dikes with basalt and chert screens west of Matogak River mouth, as thick sills intruding chert at Pyrite Point, as dikes cutting
K-Ar amphibole age of hornfels is 187 +/- 10 m.y.
Originally mapped as MzPz by Hoare abd Coonrad (1978), unit is shown as described by Box (1985) with hornfels of Hoare and Coonrad (1978) added.  Subophitic, holocrystalline plagioclase-clinopyroxene diabase (grain size to 1.5 mm). Occurs as 0.3 to 1.0-m
Trug
Upper Triassic (?) pyroxene gabbro
Altered clinopyroxene gabbro, locally up to 5 percent orthopyroxene. Augitic pyroxene (diallage) often kinked and fractured, occasionally rimmed or replaced by pale-green actinolitic amphibole. Plagioclase partially to completely replaced by fine aggrega
su
Serpentinized ultramafic rocks
Thoroughly serpentinized ultramafic rocks. Protoliths were predominately harzburgite (5-25 percent bastite pseudomorphs after orthopyroxene) with subordinate dunite and rare clinopyroxenite. Locally near Cape Newenham preserves a lineated tectonite fabri
Pzcs
Calcareous schist
Paleozoic
Schistose calcareous siltstone, limestone, and greenish tuffaceous rocks.
JTrmc
Upper Triassic-Lower Jurassic calcareous schists
Partially to completely recrystallized calcareous phyllites and schists. Protoliths include calcareous sandstones and shales, limestone conglomerates, limestone, volcanic conglomerates and mafic volcanic rocks. Clastics locally preserve turbidite feature
JTrmb
Upper Triassic-Lower Jurassic (?) metabasaltic schists
Early Jurassic (?)-Late Triassic
Partially to completely recrystallized schistose rocks with mafic igneous protoliths, including pillow basalts, angular volcanic breccia, pebbly mudstone, fine tuffaceous sedimentary rocks, diabase, gabbro, and rare chert. Greenschist to transitional gre
Two mica separates yield Late Jurassic K-Ar ages, probably resulting from Late Jurassic thermal event.
Originally shown as part of unit KJvs by Hoare and Coonrad (1978), unit shown as described by Box (1985) with hornfels from Hoare and Coonrad (1978) added.  Partially to completely recrystallized schistose rocks with mafic igneous protoliths, including p
JPvss
Permian-Jurassic (?) volcaniclastic sandstone and conglomerate
Jurassic (?)-Permian
Unit distinguished only near Goodnews Bay. Characterized by round cobble conglomerate, entirely composed of plagioclase phyric volcanic clasts, alternating with turbiditic sandstone-shale sequences. Distribution suggests it unconformably overlies Permian
Middle Jurassic K-Ar amphibole ages
JTrmvss
Upper Triassic-Lower Jurassic volcaniclastic schists
Partially recrystallized schistose rocks with sandstone, shale, and conglomerate protoliths derived from feldspar-rich volcanic source. Rounded conglomerate clasts mostly plagioclase +/- pyroxene +/- hornblende amygdaloidal porphyritic volcanic rocks, bu
Single K-Ar determination yields a Late Triassic amphibole age.
Trvs
Triassic
Marine unit consisting of chert, tuffaceous cherty rocks, argillite, siltstone, volcanic wacke, conglomerate, limestone, and mafic flows and breccias.
Pelecypods of Late Triassic age
Trb
Togiak Terrane; Pillow basalt and minor interbedded chert
Late Triassic
Massive pillow basalt and basaltic breccia interbedded with thin-bedded tuffaceous chert and shale
MzPz
Mesozoic and Paleozoic rocks, undivided
Early Cretaceous to Early(?) Ordovician
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
Limestones commonly contain Permian fossils
KCg
Gemuk Group
Chiefly massive and thin-bedded, fine-grained siliceous rocks, some volcanic rocks, calcareous siltstone, and limestone.  In the Bethel quadrangle, most probably of Jurassic, Triassic, and Permian age.
TJik
Little Kasigluk River pluton
Small masses (less than 6 km (square)) of medium-grained, hypidiomorphic granular hornblende diorite and gabbro
TrPzm
Tikchik Terrane; Melange
Triassic and Paleozoic
Structurally complex assemblage of intercalated chert, limestone, basalt, and greywacke
Fossils recovered from limestone are Permian and Late Triassic age.  Radiolarian fossils from chert are Paleozoic (?), pre-Late Devonian, Devonian (?), and Triassic ages.
KCgc
Gemuk Group, chert, siltstone, graywacke and limestone
Mississippian(?)
Massive and thin-bedded chert interbedded with siltstone and graywacke (generally calcareous), thin-bedded limestone and minor amount of mafic volcanic rocks, all of Mississippian(?) age.  Chert is black, white and gray.  No green chert, which is charact
Tectonite
MzPzc
Chert and argillite, Goodnews terrane
Mesozoic and (or) Paleozoic
White, gray-green, and blue-green recrystallized chert in 2- to 5-cm thick beds interbedded with black to dark-green phyllite or slate beds of similar thickness
Recrystallized radiolarians (Phanerozoic)
MzPzv
Goodnews Terrane; Volcaniclastic sandstone and argillite
Turbiditic, thin-bedded, medium- to fine-grained, volcaniclastic sandstone and dark-green to black argillite having weak to nonexistant slaty cleavage
MzPzs
Arkosic sandstone and slate, Goodnews terrane
Strongly cleaved, medium-grained, generally thin-bedded, arkosic sandstone and slate
TrDs
Tikchik Terrane; Marine sandstone, shale, limestone, and conglomerate
Middle (?) Triassic to Late Devonian
Well-bedded, cleaved sandstone, shale, thin limestone interbeds, and cobble conglomerate
Conodont collection of Middle (?) Triassic and Late Devonian to Early Mississippian ages
MzPza
Goodnews Terrane; Argillaceous melange with blocks of limestone, basalt, and chert
Argillaceous melange of black to green, weakly to intensely fracture foliated argillite with discontinuous phacoids of recrystallized radiolarian chert and limey sandstone
Permian pelecypods and Permian conodonts
Show by extension from Box and others, 1993.  Argillaceous melange of black to green, weakly to intensely fracture foliated argillite with discontinuous phacoids of recrystallized radiolarian chert and limey sandstone
MzPzp
Goodnews Terrane; Chloritic Phyllite
Relatively homogeneous unit of finely foliated and crenulated phyllite
MzPzm
Goodnews Terrane; Metachert and Phyllitic Metachert
Finely crystalline, thin-bedded quartzites (metachert) and finely interlayered quartzite and black phyllite
MzPzb
Metabasalt and minor metachert, Goodnews terrane
Weakly to strongly foliated metabasalt having variable recrystallization to greenschist-facies assemblage of albite-epidote-chlorite-actinolite.  Interbedded sequences of thin-bedded, white to green metachert having white mica-rich laminae.  Mid-ocean ri
Metamorphic cooling constrained to Late Jurassic or Early Cretaceous time based on K/Ar age of 146.0+15.0 Ma from actinolite
DOs
Schist and metachert
Devonian(?) to Ordovician(?)
Massively bedded green amphibole and chlorite schist interbedded with metachert; overlain by crystalline limestone, phyllite, and minor amounts of chlorite, graphite, and quartz-sericite schists.
Pl
Limestone
Permian
Thin, widespread, fine-grained, crystalline limestone.  Fetid odor.  Generally tuffaceous, locally cherty.
Permian limestone
Massive recrystallized gray limestone with fetid odor of H2S upon breaking. Weak fracture cleavage masks bedding. Occurs as large blocks along low-angle fault between schistose rocks to northwest and mafic igneous rocks southeast of Kinegnak River. Age g
Age given by shell fragments of Atomodesma sp.
KCgl
Limestone and calcareous siltstone and sandstone
Massive and thin-bedded, partly recrystallized, cream-colored limestone, estimated 500 to 1,000 feet thick near Chaekuktuli Lake; near Chikuminuk Lake, consists of interbedded gray silty limestone and calcareous siltstone and sandstone.
Invertebrate fossils reported by Mertie (1938)
Gemuk Group, limestone and calcareous siltstone and sandstone
Conprises a belt of calcareous rocks of Permian age stratigraphically underneath but grading upward into the volcanic sequence.  Near Lake Chaekuktuli, the rocks are massive and thin-bedded, partly recrystalized, cream-colored limestone, estimated to be
Pvs
Permian volcaniclastic rocks
Volcaniclastic sedimentary rocks, ranging from coarsely bedded volcanic breccias to finely bedded calcareous tuffaceous rocks. Limestone cobble conglomerate locally north of Goodnews Bay. Red to black laminated argillite with radiolarian ghosts locally n
Red to black laminated argillite with radiolarian ghosts locally north and east of Goodnews Bay. Age constrained by several occurrences of fragmentary Atomodesma sp.
Red to black laminated argillite with radiolarian ghosts locally north and east of Goodnews Bay. Age constrained by several occurrences of fragmentary Atomodesma sp. Prehnite-pumpellyite facies.
Pv
Unit consists of basalt flows, breccias, and a few sandy tuffs.  Basalts are mostly amygdaloidal and mildly altered.  Unit includes columnar-jointed flows and pillow basalts interbedded with pillow breccias.  Volcanic rocks grade downward into fossilifer
Pb
Permian (?) pillow basalt
Permian (?)
Pillow basalts, associated breccias and diabasic intrusive. Interbedded with Pvs unit. Prehnite pumpellyite facies.
Pillow basalts, associated breccias and diabasic intrusive. Interbedded with Pvs unit. Prehnite pumpellyite facies.  Revision of Hoare and Coonrad (1978) based on Box (1985).  Also, volcanic rocks separated from unit MzPz of Hare and Coonrad (1978).  Tha
KCgv
Gemuk Group, volcanic rocks
Triassic(?) and Permian
Predominantly altered dark-green to almost black mafic volcanic rocks of Permian age having abundant amygdules.  Volcanic breccia, calcareous tuff, and pillow lava make up basal part of section.  Pillow lavas also occur elsewhere in section.  Thin-bedded
Fossils of Permian age in limestone southeast of quardangle below unit and of questionable Triassic age in the Eek Mountains to south of quadrangle
Permian(?)
Predominantly  altered mafic volcanic rocks of Permian age; dark-green to almost black with abundant amygdules, few identifiable phenocrysts.  Volcanic breccia, calcareous tuffs, and pillow lava constitute basal beds.  Lavas with well-formed pillow struc
MDv
Tikchik Terrane; Massive volcanic and volcaniclastic rocks
Early Mississippian and (or) Late Devonian
Weakly to moderately foliated and flattened pillowed and massive basalt, andesite, dacite, and rhyolite flows and breccia with greenschist-facies metamorphic-mineral assemblages
Mississippian fossils
MDm
Marble and metabasaltic dikes, Goodnews terrane
Light-gray to white calcitic and dolomitic marble cut by premetamorphic basaltic dikes.  Rare metamorphic blue amphiboles (magnesioriebeckite) in metabasalt dikes indicate relatively high pressure, low temperature metamorphism
Age constrained by conodonts of latest Devonian to earliest Mississippian age
Schist and metachert -- limestone
Limestone mapped speparately in massively bedded green amphibole and chlorite schist interbedded with metachert; overlain by crystalline limestone, phyllite, and minor amounts of chlorite, graphite, and quartz-sericite schists.
DOl
Devonian to Ordovician
Thin-bedded to massive, fine-grained, highly fractured limestone.  Local interbedded tuffs and mafic volcanic rocks.  Locally recrystallized to marble.
Sparse fossils of Early to Middle Devonian age and Early (?) Ordovician age.
Dl
Devonian limestone
Devonian
Poorly exposed white limestone at southwest end of larger belt of fossiliferous Devonian shallow marine limestone (Hoare and Coonrad, 1978a).
fossiliferous Devonian shallow marine limestone.
pCl
Marbleized limestone
Precambrian
White, gray, and brownish, locally garnetiferous marbleized limestones
pCk
Metamorphic rocks of Kanektok River region
Gneiss and schist in the Kanektok River region.  Sedimentary, volcanic, and plutonic rocks metamorphosed in the upper greenschist and lower amphibolite facies.  Consists of medium- to coarse-grained, massive, and well-foliated biotite-hornblende gneisses
K/Ar ages as old as 2,000 m.y. from biotite and hornblende
Xo
Amphibolite-facies orthogneiss and amphibolite with minor intercalated pelititc schist, Kilbuck terrane
Early Proterozoic
Strongly lineated and foliated, muscovite, biotite-muscovite, or amphibole orthogneiss with granite to tonalite to diorite protoliths.  More extensively exposed in Goodnews Bay quadrangle, where it also includes amphibolite and minor pelitic schist
Two U/Pb age of igneous protolith of 2.06 Ga from zircon.  Nd/Sm isotopic systematics indicate that the rocks formed at 2 Ga.  Amphibolite-facies metamorphism U-Pb age of 1.78 Ga from sphene.  Cretaceous overprinting of most K/Ar ages suggest thermal/dyn
pCm
Metamorphic complex
preCambrian
Coarse-grained pink gneiss and medium- to coarse-grained light- to dark-gray schist constituting a sequence of highly sedimentary, volcanic, possibly some intrusive rocks