Quaternary
Gravel and sand eroded from the underlying bedrock platform and silt and sand alluvium eroded from upland areas.  
Location and physiographic expression-Active beach and bar deposits located along the present shoreline and former beach and bar deposits t
Qs
Beach, bar, and alluvial deposits
SL003
Till and outwash gravel of probable late isotope 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 an
Qg
Glacial drift
Flat-lying to gently dipping lava flows and interlayered tuffs and breccias composed chiefly of alkali-olivine basalt, olivine-bearing tholeiite, and minor amounts of basanite, hawaiite, and nephelinite (Moll-Stalcup, 1994; Wirth and others, 2002).  Nume
Qb
Basalt
early Teritary
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 outcrops are badly slumped.  Total thickness probably does not excee
Ts
Sandstone, coal, and tuff
early Tertiary
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, an
Tr
Rhyolitic and dacitic tuffs
early Tertiary and latest Cretaceous(?)
Sodium-rich 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, small hypabyssal bodies of rhyolite,
TKsr
Sodium-rich rhyolite and basalt
Tertiary and (or) Cretaceous
Flows, tuffs, and hypabyssal intrusive rocks that range in composition from basalt to rhyolite and are commonly altered.  Age is uncertain but probably no older than Cretaceous 
Location-Exposures of this unit occur at several widely scattered localities
TKv
Volcanic rocks, undivided
Cretaceous
Wide variety of flows and hypabyssal intrusive and volcaniclastic rocks.  Igneous rocks range from basalt to rhyolite in composition, but chiefly composed of andesite and trachyandesite.  Volcaniclastic rocks vary from lithic and crystal tuff and breccia
Kv
Andesitic volcanic rocks
Late and Early Cretaceous
Granite and subordinate granodiorite, monzonite, syenite, and alaskite.  The rocks vary from coarse- to fine-grained and in texture from granitic to porphyritic and seriate.  Three broad categories are recognizable:  (1) granite, granodiorite, and monzon
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 (table 1) from this unit
Ko
Olivine-bearing monzodiorite
Medium- to coarse-grained granitic textured nepheline syenite with K-feldspar phenocrysts as much as 4 cm long.  Rock-forming minerals are K-feldspar, nepheline, biotite, and melanite garnet and subordinate amounts of sodic andesine and hornblende.  Acce
Kn
Nepheline syenite
Triassic
Unit consists of an upper member, 50 m thick, composed of black shale, dark thin-bedded limestone, and chert and a lower member, 70 m thick, composed of thin-bedded chert and dark siltstone.  The upper member contains flat clams Daonella, Halobia, and Mo
Trs
Shale, limestone, and chert
Triassic and Permian(?)
Dark fine-grained to gritty carbonaceous graywacke, dark carbonaceous shale, and subordinate bedded chert and siliceous mudstone.  Clasts in graywacke consist mainly of quartz but also include plagioclase, K-feldspar, shale, chert, granitic rocks, quartz
TrPs
Graywacke, grit, and shale
Rusty-weathering altered gabbro and diabase and subordinate amounts of siliceous mudstone, laminated tuff, basalt, fine-grained graywacke, and slate.  Gabbro and diabase consist mainly of clinopyroxene, plagioclase, hornblende, and opaque minerals with m
TrPg
Gabbro and diabase
Late Mississippian
Unit composed of an upper and lower member.  Upper member consists chiefly of light- to medium-gray coarsely bioclastic limestone that contains interbedded limey mudstone in upper part.  Lower member composed of dark-gray thin-bedded limestone that conta
Mi
Limestone
Devonian
Medium-gray to brown, laminated, locally brecciated dolostone and dolomitic limestone.  Grades into dark, fine-grained, thin-bedded dolomite in upper part.  Unit metamorphosed to sugary-textured marble along contacts with granitic plutons.  The total thi
Dd
Dolostone and dolomitic limestone
Paleozoic(?)
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.  Calc-silicate hornfels composed chiefly of carbonate, scapolit
Pzu
Calc-silicate hornfels