Quaternary
Surficial deposits. Thin cover of beach, bar, and alluvial deposits, inculuding gravel, sand, silt, and peat
Qs
Saint Lawrence
Unconsolidated
SL002
Surficial deposits
Glacial drift along north coast between Akeftapak Bay and Kangee Camp.  Till and outwash of Illinoian age
Qsg
Glacial drift
Pleistocene
Nearly flatlying basalt flows. Fresh medium- to dark-gray alkali olivine basalt in massive columnar jointed flows
Qb
K/Ar age of 0.238 to 1.46 m.y.
Igneous
Basalt
Oligocene
Poorly sorted sandstone, grit, and conglomerate, carbonaceous mudstone, ashy tuff, volcanic breccia, and seams of lignitic coal
Plant fossils
Ts
Sedimentary
Sandstone, coal, and tuff
Rhyolitic and dacitic tuffs. Chiefly pale-reddish-orange to gray welded tuff, ash-fall tuff, tuff breccia, and flows of felsic composition
Abundant plant fossils
Tr
K/Ar age of 39.3 m.y.
Rhyolitic and dacitic tuffs
Paleocene
Light-gray to drab unaltered soda rhyolite flows composed of large phenocrysts of twinned sanidine and reddish brown hornblende in a fine-grained trachytic groundmass. Fine-grained dark basalt
Tsr
K/Ar of 62.1 and 64.4 m.y. on hornblende and sanadine and 64.0 m.y. on whole-rock aample of trachyte
Soda rhyolite and basalt
Tertiary and (or) Cretaceous
Scattered exposures of flows, tuffs, and hypabyssal intrusive rocks. Composition range of basaltic to rhyolitic
TKv
Undifferentiated volcanic rocks
Cretaceous
Chiefly quartz monzonite but includes granodiorite, monzonite, syenite, and alaskite
Kq
K/Ar age of 93.5 to 108 m.y.
Quartz monzonite
Nepheline Syenite. Light- to medium-gray medium- to coarse-grained granitic to seriate textured rock with k-spar phenocrysts
Kn
Nepheline Syenite
Olivine-bearing syenodiorite. Medium to dark greenish gray, coarse to medium grained, and granitic textured.
Ko
Olivine-bearing syenodiorite
Andesitic volcanic rocks. Flows, hypabyssal intrusive rocks, and volcaniclastic rocks. Cheifly andesitic and latitic in composition, but range from basaltic to rhyolitic. Locally altered to hornfels near plutons
Kv
K/Ar of 90.9 m.y. from crystal tuff
Andesitic volcanic rocks
Late and Middle Triassic
Upper member: Black shale, dark thin-bedded limestone, and chert. Lower member: Thin-bedded chert and dark siltstone. Locally altered to hornfels near plutons
Daonella, Halobia and Monotis clams
Trs
Shale, limestone, and chert
Triassic and Permian
Fine-grained to gritty dark carbonaceous graywacke and dark carbonaceous shale. Deformed and sheared. Locally altered to hornfels near plutons
TrPs
Assigned to Etivluk Group
Graywacke, grit and shale
Dark-greenish-gray rusty weathered altered gabbro and diabase
TrPg
K/Ar ages of 221 and 244 Ma
Gabbro and diabase
Late Mississippian
Lower member: Dark-gray thin-bedded limestone with abundant dark chert nodules. Upper member: Light- to medium-gray medium to coarsely bioclastic limestone. Contact metamorphosed to marble near plutons
Coral, brachiopods, and foraminiferal fauna of Late Mississippian age including Gigantoproductus, Lithostrotionella, and endothyrids
Ml
Limestone
Late and Middle Devonian
Medium-gray to brown laminated, locally brecciated dolomite and dolomitic limestone. Contact metamorphosed to marble near plutons
Stromatoporoid (Amphipora?), tabulate corals (Favosites and thamnoporoid forms), atrypids (Atrypa and Spinatrypa), spiriferoids (Koziowskiellisia? sp. and Mucrospirifera? sp.) and Coelocaulis-like gastropod
Dd
Dolomite and dolomitic limestone
Paleozoic or Precambrian
Highly crenulated banded, thick layers of pale-gray, green, and lavender calc-silicate hornfels alternating with thin layers of dark argillaceous hornfels
PzpCc
HFS
Metamorphic
Calc-silicate hornfels
Unit composed of gravel and sand eroded from the underlying bedrock platform and silt and sand alluvium eroded from upland areas.  Location and physiographic expression-Unit includes active beach and bar deposits along the present shoreline and former be
SL003
Beach, bar, and alluvial deposits
Till and outwash gravel of probable late isotpe stage 5 or  isotope stage 4 (early Wisconsin) age deposited by an ice sheet that extended across the Bering Sea shelf from the Chukotsk Peninsula in northeastern Russia to Saint Lawrence Island (Hopkins and
Qg
early Tertiary
Poorly consolidated sandstone, grit and conglomerate, carbonaceous mudstone, ashy tuff, volcanic breccia, and seams of lignitic coal as much as 60 cm thick.  Unit is poorly exposed and badly slumped.  Total thickness probably does not exceed 25 m.  Abund
Flat lying to gently dipping lava flows and interlayered tuffs and breccias composed chiefly of alkali olivine basalt, olivine tholeiite, and minor amounts of basanite, hawaiite, and nephelinite (Moll-Stalcup, 1994). Numerous small cinder cones and flows
Pale-reddish-orange to gray welded tuff, ash-fall tuff, tuff breccia, and flows of felsic composition (Patton and Csejtey, 1980).  On Fossil River unit contains a thin sequence of quartzose sandstone, quartz-chert conglomerate, volcanic conglomerate, and
early Tertiary and latest Cretaceous
Soda rhyolite flows composed of large phenocrysts of twinned sanidine and reddish-brown hornblende in a fine-grained trachytic groundmass.  Unit locally includes basalt, trachyandesite, and andesite, lava flows and small hypabyssal bodies of rhyolite, an
TKsr
Unit composed of flows, tuffs, and hypabyssal intrusive rocks that range in composition from basaltic to rhyolitic and are commonly altered.  Age is uncertain but probably no older than Cretaceous.  Location-Exposures of this unit occur at several widely
Volcanic rocks, undivided
Late and Early Cretaceous
Unit composed of granite and subordinate granodiorite, monzonite, syenite, and alaskite.  The rocks vary in texture from coarse to fine-grained and from granitic to porphyritic and seriate.  Three broad categories are recognizable: 1) granite, granodiori
Kg
Granite and granodiorite
Early Cretaceous
Monzodiorite composed of a medium- to coarse-grained granitic textured rock composed chiefly of plagioclase, K-feldspar, augite, olivine, and biotite.  Accessory minerals include apatite, zircon, and magnetite.  A biotite sample from this unit yielded an
Olivine-bearing monzodiorite
A medium- to coarse-grained granitic textured rock with K-feldspar phenocrysts as much as 4 cm long.  Rock-forming minerals are K-feldspar, nepheline, biotite, and melanite garnet with subordinate amounts of sodic andesine and hornblende.  Accessory mine
Nepheline syenite
Unit includes a wide variety of flows, hypabyssal intrusive rocks and volcaniclastic rocks composed chiefly of andesite and trachyandesite but range from basalt to rhyolite.  Volcaniclastic rocks vary from lithic and crystal tuffs and breccias to volcani
Triassic
Unit consists of an upper member, 50m thick, composed of black shale, dark thin-bedded limestone, and chert; and a lower member, 70m thick, composed of thin-bedded chert and dark siltstone.  The upper member contains flat clams, Daonella, Halobia, and Mo
Shale, limestone, and chert, Ongoveyuk terrane
Unit composed of an upper and lower member. The upper member consists chiefly of light- to medium -gray coarsely bioclastic limestone that contains interbedded limey mudstone in the upper part.  The lower member is composed of dark-gray thin-bedded limes
Assigned a Late Mississippian age on the basis of an abundant coral, brachiopod, foraminifera, and conodont fauna (Patton and Dutro, 1969) (Lane and Ressmeyer, 1985) (Zhang and Blodgett 2007)
Limestone, Ongoveyuk terrane
Devonian
Medium-gray to brown, laminated, locally brecciated dolomite and dolomitic limestone.  Grades into dark, fine-grained, thin-bedded dolomite in upper part.  Unit metamorphosed to a sugary-textured marble along contacts with granitic plutons.  The total th
Assigned a probable Late and Middle Devonian age on the basis of an abundant fauna that includes Amphipora (?), tabulate and thamnoporoid corals, and assorted brachiopod species (Patton and Dutro, 1969) (Zhang and Blodgett, 2007)
Dolostone and dolomitic limestone, Ongoveyuk terrane
Triassic and Permian?
Unit composed of dark fine-grained to gritty carbonaceous graywacke, dark carbonaceous shale, and subordinate bedded chert and siliceous mudstone. The graywacke clasts consist mainly of quartz but also include plagioclase, K-feldspar, shale, chert, grani
Graywacke, grit, and shale, Tomnamie terrane
Unit composed of rusty-weathering altered gabbro and diabase and subordinate amounts of siliceous mudstone, laminated tuff, basalt, fine-grained graywacke, and slate.  The gabbro and diabase consist mainly of clinopyroxene, plagioclase, hornblende, and o
Gabbro and diabase, Tomnamie terrane
Paleozoic?
Unit composed of a highly crenulated banded rock consisting of 0.5- to 10-cm-thick layers of pale gray, green and lavender calc-silicate hornfels alternating with thinner layers of dark argillaceous hornfels.  The calc-silicate hornfels is composed chief
Pzu