Qs
HC002
Surficial deposits, undifferentiated
Includes flood plain deposits of silt, sand, and gravel, and fluvial, colluvial, and eolian terrace and slope deposits of silt and very fine sand.
Quaternary (Holocene and Pleistocene)
Holy Cross
Unconsolidated
Qof
BL002
Old flood-plain deposits
Flood-plain deposits of silt, sandy silt, and bog deposits
Quaternary
Black
HP002
Old flood-plain and delta deposits
Old flood-plain and delta deposits; silt, sandy silt, and bog deposits
Hooper Bay
SC002
Old flood-plain deposits, mostly silt and sandy silt
Saint Michael
Qoa
Old alluvial deposits
Old alluvial deposits; mostly silt and sand; clay and minor amounts of fine gravel at depth.  Mostly fluvial with some wind deposits
Alluvial deposits of silt and sandy silt overlying sand and gravel.  Includes terrace and fan gravel and colluvial deposits
Qgc
Glacial and colluvial deposits
Glacial and colluvial deposits; sand, gravel, boulders, and angular talus blocks.  Includes steep recent fans of gravel and boulders
Qu
RM004
Quaternary deposits, undifferentiated
Unconsolidated alluvial, colluvial, and eolian deposits
Russian Mission
Qac
HP003
Alluvial, colluvial, and glacial drift deposits, undivided
Alluvial and colluvial deposits consist mainly of silt, sandy silt, and peat.  Alluvium is chiefly fluvial in origin, but locally includes reworked windblown deposits.  Glaical drift composed of sand, gravel, and boulder morainal and outwash deposits
SC003
MA003
Marshall
HC003
RM005
KW003
Kwiguk
KW002
Alluvial deposits of silt and sandy silt on the delta with sand and gravel at depth; also includes terrace and fan gravel and colluvial deposits in and near mountains
Qyf
Younger flood-plain deposits
Flood-plain depoits of silt and sandy silt on sand delta; also includes gravel and boulders in and near mountains
Qf
RM002
Flood Plain Alluvium
Flood plain alluvium
MA002
Young flood-plain deposits
Young flood-plain deposits; silt and sandy silt, minor sand and gravel
Beach and lagoon deposits, mostly silt and sandy silt on the delta; includes gravel and boulders in and near Nulato Hills
Qa
RM003
Alluvium
Unconsolidated alluvial, colluvial, glacial outwash, lucustrine, and eolian conglomerate, sand, silt, and mudrock
Russian Misson
Qe
Estuarine deposits
Estuarine deposits; fluvial silt and sandy silt, reworked and deposited by tidal currents and wave action
Old flood-plain deposits; silt and sandy silt
Old alluvial deposits; chiefly silt and sandy silt with sand and gravel at depth.  Includes terrace and colluvial deposits near mountains
Sandy flood-plain alluvium
Sandy flood-plain alluvium.  Unconsolidated, well stratified, gray- to tan-weathered fine-grained sand, silty sand, and silt deposited by modern streams
Quaternary (Holocene)
Qag
Coarse-grained, gravel-rich alluvium
Coarse-grained, gravel-rich alluvium.  Unconsolidated, moderately- to well stratified silt, sand, and gravel deposited by modern streams
Qas
Flood-plain alluvium with extensive overbank deposits
Flood-plain alluvium with extensive overbank deposits.  Alluvium composed of interbedded, dark-brown-gray, organic-rich sand and sandy silt.  Masks Qa and Qag
Qgr
Reworked glacial outwash and till deposits
Reworked glacial outwash and till deposits.  Well sorted, moderately well-stratified sand and pebble gravel reworked from coarser outwash gravel and diamicton by perennial streams
Floodplain, tidal flats, and estuarine deposits
Unit composed cheifly of silt, fine sand, and peat.  Some gravel and coarse sand depoists occur locally along the tributary streams draining upland areas.  Estuarine deposits conists of fluvial silt and sandy silt that has been reworked and redeposited b
Qaf
Alluvial fan deposits
Alluvial fan deposits.  Generally poorly sorted, partially stratified sand and coarse gravel deposits
Qctf
Fan and terrace deposits
Fan and terrace deposits.  Composite unit of poorly sorted, partially stratified silt, sand, and gravel of alluvial and colluvial fans
Qc
Colluvium
Chiefly frost-rived rubble, locally includes stream alluvium, terrace gravel, glacial deposits, and wind blown silt
Qca
Colluvial-alluvial deposits
Colluvial-alluvial deposits.  Poorly to moderately well-sorted silt, sand, gravel, and diamictin of alluvial, colluvial, and locally, glacial origin
Qct
Talus
Talus.  Angular fragments of frost-riven bedrock transported downslope by gravity and deposited as apron or fans at toe of slope.
Qat
Terrace alluvium
Terrace alluvium.  Well-sorted, moderately stratified gravelly sand and silt
Qrs
Reworked Silt
Silt, sandy silt, and bog deposits
Qyb
Younger beach deposits
Beach deposits of marine silt and sandy silt and younger flood-plain and estuarine deposits along streams
Young beach deposts
Young beach deposts; marine silt, sandy silt, and sand.  Forms beaches, spits, bars, dunes, and islands
Qbl
Beach and lagoon deposits
Beach and lagoon deposits, mostly silt and sandy silt
Qob
Old beach deposits
Old beach deposits; marine silt and sandy silt forming older beach ridges and intervening swales
Beach and lagoonal deposits
Silt and sandy silt.  Deposits form the modern offshore bars, spits, and beach ridges.
Beach deposits of marine silt and sandy silt
BL003
Estuarine deposits; silt and sandy silt
Qw
Wind-blown deposits
Wind-blown deposits; silt and sandy silt
Silt and sandy silt.  Deposits form broad partly dissected stabilized dune fields in the lowlands of the Yukon and Kuskokwim Rivers.  The dune fields overlie the alluvial and colluvial deposits of unit Qac and predate the floodplain deposits of unit Qf.
Qsw
Wind-deposited Silt
Wind-deposited silt
Silt Deposits
Light- to dark-gray silt and sandy silt
Qsp
Silt and peat
Silt and peat.  Poorly stratified, black to brown, organic-rich alluvial, lacustrine, or bog silt.
Qd
Glacial Drift
Poorly sorted sand, gravel, and boulders; stipples (of original map) indicate well defined end and lateral moraines
Qt
Glacial till
Unconsolidated glacial till; ground lateral and end moraines
Quaternary (Pleistocene)
Qrg
Rock-glacier deposits
Rock-glacier deposits.  Stable, tongue-shaped mass of unsorted, angular frost-shattered boulders and cobbles.
Qgt4
Till
Till.  Unmodified till from Crater Mountain glaciation of early Holocene(?) age
Qgt3
Till, Tolstoi Lake glaciation
Till consisting of fresh, undissected moraines from Tolstoi Lake glaciation of late Wisconsin age
Quaternary (Late Pleistocene)
Qgt2
Till, Bifurcation Creek glaciation
Till consisting of dissected moraines from Bifurcation Creek glaciation of late Wisconsin age
Qo
Outwash Deposits
Poorly- to well-sorted silt, sand, gravel, and boulders in terraces and outwash fan-plains
Qgf
Outwash-fan deposits
Outwash-fan deposits.  Poorly consolidated, moderately well-stratified sand and gravel deposited as large fans proximal to ice-marginal meltwater streams during Late Pleistocene
Qgt1
Till, Beaver Creek glaciation
Till.  Reworked, highly dissected till from Beaver Creek glaciation of pre-Wisconsin age
Quaternary (Early Pleistocene)
Qb
Basalt
Basalt; undeformed flows and associated cones and craters.  Includes pyroclastic rock
Age based on magnetic polarity
Igneous
Qby
Basalt; Younger flows and cones
Basalt flows
Columnar-jointed flows of fine-grained tholeiitic and alkaline-olivine basalt
Horizontal basalt flows and associated colcanic craters
QTb
Horizontal vesicular basalt flows
Quaternary and Tertiary
Olivine basalt and associated scoria
Age determined from paleomagnetic
Qbo
Basalt; Older flows, cones, maars, tuffs, and breccias
Part of the late Cenozoic Bering Sea basalt province.  Vesicular tholeiitic and alkali basalt lava flows, cones, and maar craters.  The flows are interlayered with subordinate amounts of pyroclastic deposits that range from fine ash to coarse breccia.  T
Quaternary and latest Tertiary
K-Ar ages ranging from 3.25 Ma to 0.19 Ma from samples in the Unalakleet quadrangle
Tr
Albite Rhyolite
Light- to medium-gray, fine-grained, porphyritic rhyolite; occurs as small stock or pluglike intrusive bodies
Tertiary
Tb
Three small areas of basalt lava flows.  Two on the Yukon River in the northwestern part of the quadrangle and one on the Owhat River in the northeastern part of the quadrangle.  Flat-lying vesicular basalt
Late Tertiary
Whole-rock K-Ar ages of 19.35 Ma and 6.19 Ma
Tvb
Medium- to dark-gray, vesicular olivine-clinopyroxene basalt and minor basaltic andesite
late Tertiary (late Pliocene)
Whole rock K/Ar of 6.19 Ma
Tm
Mafic volcanic and subvolcanic rocks, undifferentiated
Wide variety of of basaltic and andesitic flows, agglomerate, coarse breccia, fine-grained tuff, and subordinate hypabyssal intrusive rocks.  Most common is olivine basalt and pyroxene andesite
Tertiary (Eocene and Paleocene)
Tfu
Felsic volcanic and subvolcanic rocks, undifferentiated
Flows, tuffs, breccias, and fine-grained hypabyssal intrusions, ranging in composition from rhyolite to dacite.
K-Ar in the Unalakleet quadrangle
Tfi
Felsic hypabyssal intrusives
Known or strongly suspected fine-grained felsic hypabyssal intrusive rocks of unddifferentiated unit Tfu
Tg
Granitic Rocks
Medium- to coarse-grained, pink and gray granitic-textured rocks.  Forms stocks chiefly of quartz monzonite, but ranges from granodiorite to granite; minor facies include gabbro, diabase, and aplite.
Ti
Intrusive Rocks (?)
Probable stocks of granitic rocks; interpreted and mapped by photogeologic methods.
Mafic Rocks
Medium- to coarse-grained, light- to dark-gray gabbro and diabase.  Occurs as small stocklike bodies, dikes, and sills.
Tgr
Shallow granitic intrusives
Small epizonal granitic intrusive rocks, inferred to range from granite to tonalite, be fine- to coarse-grained, and having varying textures.  Locally sheared or brecciated..
TKuv
Volcanic Rocks
Probably andesitic lava for the most part, with some interbedded sedimentary rocks; interpreted and mapped by photogeologic methods.
Tertiary and Cretaceous
TKvt
Andesite to dacite flows and tuff
Andesite to dacite flows and tuff.  Medium-green-gray, very fine-grained, porphyritic biotite andesite to dacite flows.  Light-green-gray, platy-weathering, fine- to medium-grained crystal-lithic tuff.
early Tertiary and (or) Late Cretaceous
TKva
Volcanic agglomerate
Volcanic agglomerate. Medium- to dark-green-gray, lapilli tuff and agglomerate containing elliptical bombs and subangular to rounded fragments of andesite.
ALT
TKad
Dacite, rhyolite, andesite, and basalt lava flows, and volcaniclastic and hypabyssal rocks, undivided
Dacite, rhyolite, andesite, and basalt lava flows, and volcaniclastic and hypabyssal rocks, undivided
Confined to the Holy Cross quadrangel and northern part of the Russian Mission quadrangle where field data are insufficient to map units TKa and TKd sep
early and late (?) Tertiary and latest Cretaceous
Dacite, rhyolite, andesite, and basalt lava flows, and volcaniclastic and hypabyssal rocks, undivided.  Confined to the Holy Cross quadrangel and northern part of the Russian Mission quadrangle where field data are insufficient to map units TKa and TKd s
HFS
TKhf
Hornfels
Formed in the thermal aureole bordering the granitic cores of the Fox Hills and Russian Mountains.  Consists of metasiltstone, metasandstone, metaconglomerate and subordinate amounts of metavolcanic rocks
early Tertiary and latest Cretaceous
Metamorphic
TKdf
Dikes and small hypabyssal intrusions
Dikes and small hypabyssal intrusions.  Fine-grained, locally porphyro-aphanitic biotite quartz porphyry.
TKi
Shallow intrusive rocks of intermediate and silicic composition
Composed of rhyolite, dacite and lesser amounts of trachyte and andesite.  The typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende.
U/Pb zircon age of 63.6 Ma, 40Ar/39Ar age of 67.3 Ma, 40Ar/39/Ar age of 65.7 Ma
TKvi
Andesite to dacite
Andesite to dacite.  Poorly exposed, light- to medium-green-gray, porphyro-aphanitic pyroxene andesite to dacite flows.
TKd
Dacite and rhyolite lava flows, domes, and volcaniclasic and hypabyssal rocks
Dacite, rhyolite, and subordinate trachyandesite lava flows, sills, dikes, and interlayered tuffs, ash-flow tuffs, and breccias.  Flows generally are porphyritic and composed of phenocrysts of plagioclase, sanidine, quartz, and biotite in a fine-grained
early Teritiary and latest Cretaceous
K-Ar ages of 67.0 Ma and 64.7 Ma from an area mapped as TKad
TJb
Whitefish Lake Volcanic Field
Altered basaltic lava flows and subordinate altered andesite, dacite, rhyolite, and gabbro.  Inferred to be the extrusive equivalent of the mafic intrusive rocks of unit TJm.  Regional relationships suggest unit could be as old as Jurassic or as young as
early Tertiary to Jurassic
TJwl
Whitefish Lake volcanic field, Nyac terrane
Highly altered basaltic flows, subordinate altered andesite, dacite, rhyolite, and gabbro.  Lavas believed to be extrusive equivalent of parts of diorites and gabbros (TJim) of Nyac Terrane
early Tertiary?, Cretaceous, and Jurassic?
Sedimentary
Q
TKa
Andesite and basalt flows and volcanicclasitc rocks
Composed primarily of andesite and basalt lava flows and volcaniclastic rocks.  Flows are generally porphyritic and composed of phenocrysts of plagioclase and pyroxene in a groundmass of plagioclase microlites.  Volcaniclastic rocks include breccia, tuff
K-Ar ages of 50.8 and 42.9 Ma
Five K-Ar ages of 65.2 to 51.9 Ma in the Unalakleet quadrangle
K-Ar ages of 50.8 and 42.9 Ma.  Five K-Ar ages of 65.2 to 51.9 Ma in the Unalakleet quadrangle
TKda
Dikes and small hypabyssal intrusions.  Medium-green-gray, very fine-grained to porphyro-phanitic biotite-axinite andesite porphyry.
TKdm
Dikes and small hypabyssal intrusions.  Olivine-rich, fine-grained gabbro to picrite with distinctive columnar jointing.
TKmp
Porphyritic quartz monzonite
Porphyritic quartz monzonite.  Light gray, locally bleached, fine-grained to porphyro-aphanitic, clinopyroxene-bearing, biotite-rich quartz monzonite.
TKg
Granite, granodiorite, syenite, and monzonite
Composed of plutonic rocks that have been assigned a wide variety of petrographic names based largely on field inspection and examination of a few thin sections.  The most common rock type appears to be biotite granite, but other rock types include grano
Seven K-Ar cooling ages from this unit range from 70.9 to 60.9 Ma
TKsy
Quartz syenite
Quartz syenite.  Medium-gray, medium-grained, equigranular, biotite-rich quartz syenite.
TKsym
Syenite to monzonite and quartz monzonite
Syenite to monzonite and quartz monzonite.  Medium-gray, subporphyritic, biotite-pyroxene syenite to monzonite and quartz monzonite.  Transitional between TKsy and TKmp.
Biotite-pyroxene quartz monzonite yielded K/Ar of 70.3 Ma
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
TJgd
Gabbro and diorite
Tertiary, Cretaceous, and Jurassic
TJm
Altered mafic plutonic rocks
Altered gabbro and diorite bodies.  Intrudes units Jab, Jvc, KJv, and KMu.  Age of unit is uncertain, but not older than Jurassic.  Some or all of the unit may be as young as Tertiary
Gabbro and diorite   Unit dropped, now part of TJm (1682)
Kym
Polymict conglomerate, sandstone, siltstone, and shale
Yukon-Koyukuk basin
Marginal shelf and slope deposits
Composed of pebble and cobble conglomerate interbedded with sandstone, siltstone, and shale.  Conglomerate contains clasts of chert, greenstone, quartz, and schist in variable amounts.  Sandstone vari
Cretaceous
Well-preserved leaf impressions of Cretaceous (Albian-Cenomanian ?) age (personal communication, J.A. Wolfe, 1962)
Polymict conglomerate, sandstone, siltstone, and shale, Yukon-Koyukuk basin, Marginal shelf and slope deposits
Composed of pebble and cobble conglomerate interbedded with sandstone, siltstone, and shale.  Conglomerate contains clasts of chert, greenstone, quartz, and schist in variable amounts.  Sandstone varies from poorly sorted graywacke turbidite to well-wash
Polymict conglomerate, sandstone, siltstone, and shale, Yukon-Koyukuk basin, marginal shelf and slope deposits
Ks
Noncalcareous sandstone
Interbedded fine- to medium-grained noncalcareous sandstone and siltstone.  Local hornfels
Sandstone, shale, conglomerate, and coal
Chiefly fluvial and shallow marine deposits of well-sorted, medium- to coarse-grained, light-gray to olive, cross-bedded sandstone, fine- to medium-grained, dark-gray to green silty sandstone, dark-gray micaceous shale, quart-chert pebble conglomerate, a
Late and Early Cretaceous (Cenomanian and Albian)
Cenomanian and Albian megafossils, including plants in Unalakleet quadrangle to north.
Kks
Kuskokwim Group (siltstone)
Medium- to dark-gray siltstone and graywacke with interbeds of grit and conglomerate.
Kus
Sedimentary rocks, undifferentiated
Sedimentary rocks, undifferentiated.  Heterogeneous unit of fine to coarse, generally noncalcareous, micaceous sandstone, siltstone, and minor shale.
Late to middle Cretaceous
Kkcf
Kuskokwim Group; Chert-clast provence rocks; Outer-fan turbidite facies
Thin-bedded, fine-grained, quartzose sandstone and slate with lesser thin- and thick-bedded medium-grained sandstone.
Late Cretaceous (Turonian)
Age considered Turonian (Late Cretaceous) based on three megafossil collections
Kkmf
Kuskokwim Group; Mixed provence 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 occurances
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 occurances
Kksh
Kuskokwim Group; Shale and siltstone
Dark-gray to black, finely laminated shale, siltstone and thin-bedded, very fine grained sandstone.
Late Cretaceous (Early Turonian and (or) Late Cenomanian)
Age constrained by megafossil occurances of late Cenomanian and (or) early Turonian age low in section and by overlying units of Turonian age
Ksl
Calcareous lithic sandstone
Calcareous lithic sandstone.  Gray to tan, subangular to rounded, fine- to coarse-grained calcareous lithic sandstone and interbedded micaceous siltstone, locally plant rich.  Sandstone equivalent to the calcareous clastic units of Kuskokwim Group.
Sandstone, siltstone, and shale
Kuskokwim basin
Deltaic and submarine fan deposits, undivided
Composed of both deltaic and submarine fan deposits, but the two different facies are not mapped separately owing to the lack of field data.  The deltaic deposits consist of well-sorted, quart
Sandstone, siltstone, and shale, Kuskokwim basin, deltaic and submarine fan deposits, undivided
Composed of both deltaic and submarine fan deposits, but the two different facies are not mapped separately owing to the lack of field data.  The deltaic deposits consist of well-sorted, quartz-rich, cross-bedded sandstone interbedded with siltstone and
Hornfels Altered Kks and Tkd
Kkcd
Kuskokwim Group; Chert-clast provence rocks; Deltaic facies
Thick bedded quartzose sandstone, pebbly sandstone, and subordinate siltstone and shale.
Shaktolik Group
Interbedded sandstone, shale, "argillite," grit, and conglomerate.
Interbedded fine- to medium-grained gray noncalcareous sandstone and siltstone.  Includes both marine and nonmarine strata, and biotite-hypersthene hornfels.
Albian and Cenomanian age from plant fossils (Aralia wellingtoniana and Credneria grewiopsoides) and mollusks (Cultellus kokolikensis
Kys
Sandstone and siltstone, Yukon-Koyukuk basin, deltaic deposits
Fluvial and shallow marine deltaic depoists of sandstone, siltstone, and shale.  Locally crossbedded and ripple marked.  Yukon-Koyukuk basin, deltaic deposits
Plant debris and fresh- and brackish-water mollusks
Sandstone and siltstone
Yukon-Koyukuk basin
Deltaic deposits
Fluvial and shallow marine deltaic depoists of sandstone, siltstone, and shale.  Locally crossbedded and ripple marked
Yukon-Koyukuk Basin, Sandstone and siltstone
Sandstone and siltstone.
Sandstone and siltstone, Yukon-Koyukuk basin, Deltaic deposits
Yukon-Koyukuk basin
Deltaic deposits
Sandstone and siltstone intruded by numerous small hypabyssal bodies of rhyolite and dacite (TKi)
Kys (dot)
Sandstone and siltstone. Dot pattern where intruded by numerous small hypabyssal bodies of rhyolite and dacite (TKi)
Sandstone and siltstone and hypabyssal intrusions, Yukon-Koyukuk basin, deltaic deposits
Sandstone and siltstone intruded by numerous small hypabyssal bodies of rhyolite and dacite (TKi).  Yukon-Koyukuk basin, deltaic deposits
Kygc
Highly calcareous graywacke sandstone and mudstone turbidites, Yukon-Koyukuk basin, submarine fan deposits
Turbidites composed of highly calcareous sandstone interbedded with noncalcareous micaeous siltstone and shale.  No fossils found, but elsewhere in the Yukon-Koyukuk basin similar assemblages have yielded marine mollusks of probable late Early Cretaceou
Highly calcareous graywacke sandstone and mudstone turbidites
Yukon-Koyukuk basin
Submarine fan deposits
Turbidites composed of highly calcareous sandstone interbedded with noncalcareous micaeous siltstone and shale.  No fossils found, but elsewhere in the Yukon-Koyukuk basin similar assemblages have yielded marine
Highly calcareous graywacke sandstone and mudstone turbidites, Yukon-Koyukuk basin, Submarine fan deposits
Turbidites composed of highly calcareous sandstone interbedded with noncalcareous micaeous siltstone and shale.  No fossils found, but elsewhere in the Yukon-Koyukuk basin similar assemblages have yielded marine mollusks of probable late Early Cretaceous
Kls
Laumontitized sandstone
Mottled or spotted medium to dark gray laumontitized tuffaceous sandstone interbedded with equal or greater amounts of siltstone and sandstone and sandstone containing little or no laumontite
Mottled or spotted medium- to dark-gray laumontitized sandstone interbedded with equal or greater amount of siltstone and sandstone
Kygv
Graywacke sandstone and mudstone turbidites containing abundant laumontitized volcanic debris, Yukon-Koyukuk basin, Submarine fan deposits
Hard, well-indurated, fine- to medium-grained, locally tuffaceous, sandstone and micaceous mudstone.  No fossils found, but elsewhere in the Yukon-Koyukuk basin a lithologically similar unit has yielded marine mollusks of probable late Early Cretaceous a
Kcs
Calcareous sandstone
Mostly fine- to medium-grained, gray highly calcareous sandstone interbedded with non-calcareous siltstone with calcareous concretions
Mostly fine- to medium-grained gray, highly calcareous, thin-bedded sandstone interbedded with noncalcareous siltstone
Fine- to medium-grained highly calcareous, thin-bedded sandstone interbedded with noncalcareous siltstone
Non-calcareous sandstone
Mostly fine- to medium-grained gray, non-calcareous sandstone and dark gray to black siltstone
Interbedded sandstone and siltstone.  Thermally metamorphosed to hornfels.  Similar to Cretaceous rocks in the Kwiguk quad.
Kyg
Graywacke sandstone and mudstone turbidites, undivided, Yukon-Koyukuk basin, submarine fan deposits
Sparse field data on this sedimentary rock unit suggests that it is composed largely of graywacke turbidites and includes both highly calcareous graywacke as in unit Kygc and graywacke containing abundant volcanic debris as in unit Kygv.  Yukon-Koyukuk b
Graywacke sandstone and mudstone turbidites, undivided, Yukon-Koyukuk basin, Submarine fan deposits
Ki
Intrusive rhyodacite, dacite, and aplite
Intrusive rhyodacite, dacite, and aplite forming small, light- to dark-gray, fine-grained porphyritic dikes and sills
Intrusive rhyodacite and dacite
Light- to medium-gray, fine-grained, porphyritic rhyodacite and dacite; intrucive, forming dikes and large sill-like bodies
Late Cretaceous
Shallow granodiorite intrusives
Shallow, dominantly sill-like bodies probably ranging in composition from granodiorite to diorite.
67.1 +/- 3 and 78.7 +/- 4 Ma K-Ar ages determined on similar rocks to west of quadrangle
Kuskokwim Group (andesite)
Massive gray and greenish-gray porphyritic andesite lava flows, flow breccia, and agglomerate with some interbedded sedimentary rocks.
TKvm
Basaltic andesite and andesite
Basaltic andesite and andesite.  Medium- to dark-green-gray, aphanitic to fine-grained, pyroxene-rich basaltic andesite and andesite.
Early Tertiary and (or) Late Cretaceous
K/Ar of 75.8 Ma
Kv
Andesitic volcaniclastic rocks
Dark-greenish-gray crystal and lithic tuff, fine cherty tuff, and volcanic sandstone
Early Cretaceous (Valanginian)
Early Cretaceous (Valanginian) megafossils and radiolaria in Unalakleet quadrangle
KJv
Volcanic rocks
Volcanic rocks consisting of dark gray and green andesitic flows and volcaniclastic rocks
Jurassic? and Cretaceous
Andesitic and basaltic volcaniclastic rocks, lava flows, chert, and mudstone
Koyukuk terrane
Highly disrupted assemblage of mafic to intermediate tuff, breccia, agglomerate, volcanic-rich conglomerate and graywacke, cherty tuff, chert and mudstone and andesitic and basaltic pillow lava.  Age assigned based on sparse fossil and is
Early Cretaceous and Jurassic
Molluscks of Early Cretaceous (Hauterivian and Valanginian age)
K-Ar amphibole age of 128 Ma (Early Cretaceous)
K-Ar amphibole age of 164 Ma (Middle Jurassic)
Andesitic and basaltic volcaniclastic rocks, lava flows, chert, and mudstone, Koyukuk terrane
Highly disrupted assemblage of mafic to intermediate tuff, breccia, agglomerate, volcanic-rich conglomerate and graywacke, cherty tuff, chert and mudstone and andesitic and basaltic pillow lava of the Koyukuk terrane.  Age assigned based on sparse fossil
Molluscs of Early Cretaceous (Hauterivian and Valanginian age)
Dark-gray and green andesite flows, volcanoclastic rocks, and minor interbedded graywacke
Early Cretaceous and Jurassic?
K-Ar amphibole age of 128 Ma (Early Cretaceous), K-Ar amphibole age of 164 Ma (Middle Jurassic)
Kg
Granitic rocks
Light-gray, medium-grained, weakly foliated granitic rocks
Granodiorite
Light gray, medium- to coarse-grained, locally porphyritic granodiorite
K/Ar age of 78.7 +/- 4.0 m.y. from biotite
Granodiorite and granite
Composed chiefly of biotie granite and hornblende-biotite granodiorite.
Late and Early Cretaceous
K-Ar and 40Ar/39Ar ages ranging from 101 to 120 Ma.  U/Pb age between 104 and 129 Ma (upper Concorida intercept).  K/Ar age of 80.6 +/- 4.0 Ma
Kis
Sawpit pluton
Recessively weathering, pink-colored, coarse-grained, seriate, leucocratic biotite granite pluton.
Early Cretaceous
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
KJb
Basaltic and andesitic lava flows, Nyak terrane
Variably altered basalt and andesite.  Conformably(?) overlies unit Jab and unconformably(?) overlain by unit TJb.  Nyak terrane
Early Cretaceous to Late Jurassic
KJba
Basaltic and Andesitic lava flows, Nyac terrane
Basaltic and andesitic lava flows.
Early Cretaceous and (or) Late Jurassic
TJi
Hyabyssal felsic intrusive rocks
Altered rhyolite and dacite porphyries.  Age of unit is uncertain, but not older than Jurassic.  May be as young as Tertiary
TJih
Hypabyssal felsic intrusive rocks
Highly altered rhyolite and dacite porphyries.
early Tertiary?, Cretaceous, and Jurassic
Jvc
Volcaniclastic conglomerate, sandstone, and shale
Tuffaceous marine sandstone, shale, and conglomerate.  Minor basaltic and andesitic lava flows.  Felsic pyroclastic rocks locally near base of unit.  Unit rests conformably(?) on unit Jab and is conformably(?) overlain by unit KJb
Late and Middle Jurassic
Mollusks of Late Jurassic (late Kimmeridgian to early Tithonian) age
Volcaniclastic conglomerate, sandstone, and shale, Nyac terrnae
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)
Jt
Trondhjemite, tonalite, and gabbro
Koyukuk terrane
Composed chiefly of trondjhemite and tonalite plutonic bodies that locally have been metasomatized by potassium-rich fluids to a pink granite and granodiorite.  Also includes subordinate amounts of quarz diorite, diorite, and gabbro
Jurassic
K-Ar ages from 173 to 130 Ma in the Unalakleet quadrangle (Patton and Moll-Stalcup, 1996)
Jgr
Mafic granitoid rocks
Poorly known diorite, gabbro, and tonalite plutons intruding unit MzPzb in northern part of quadrangle
Correlative rocks in Unalakleet quadrangle yielded K-Ar age of 154 +/- 6, 166 +/- &, qnd 173 +/- ( Ma
TJim
Small, erosionally neutral, texturally and compositionally diverse, partially to extensively altered diorite and gabbro bodies
Early Tertiary?, Cretaceous, and Jurassic
Jab
Andesite and basalt, Nyac terrane
Andesite and basalt
Middle Jurassic
Andesitic and basaltic lava flows and marine volcaniclastic rocks
Andesitic and basaltic lava flows and flow breccia.  Tuffaceous sandstone and conglomerate containing abundant clasts of mafic and intermediate volcanic and intrusive rocks.  Unit altered to low-grad metamorphic facies by variable replacement of primary
Marine mollusks
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)
MzPzum
Serpentinized ulramafic rocks
Koyukuk terrane
Presumed to be composed of partly serpentinized harzburgbite and dunite.  May also include some gabbro
Mesozoic and Paleozoic?
KCgu
Gemuk Group (mafic volcanics and sedimentary rocks)
Mafic lava flows, volcanic breccia, and agglomerate interbedded with siliceous siltstone, chert, graywacke, and a small amount of calcareous conglomerate and limestone
Carboniferous? to Cretaceous
TrPvs
Metavolcanic and metasedimentary rocks
Chiefly gray and green, fine- to medium-grained schistose metavolcanic and metasedimentary rocks.  Includes contact metamorphosed hornfels
Permian and Triassic?
MzPzvs
Metasandstone, argillite, and mafic meta-igneous rocks
Metasandstone, argillite, and mafic meta-igneous rocks.  Poorly exposed, highly deformed heterogeneous package of green, feldspathic, tuffaceous metasandstone.  Dark-gray to brown argillite.  Dark-green, fine- to coarse-grained metabasalt and metadiorite
early Mesozoic to middle Paleozoic
KMu
Andesitic and basaltic volcaniclastic rocks, lava flows, chert, and mudstone (KJv) and altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone (TrMv), undivided
Undivided Koyukuk and Angayucham-Tozitna terranes
Andesitic and basaltic volcaniclastic rocks, lava flows, chert, and mudstone (KJv) and altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone (TrMv), undivided
Cretaceous to Mississippian
Undivided Koyukuk and Angayucham-Tozitna terranes
Andesitic and basaltic volcaniclastic rocks, lava flows, chert, and mudstone (KJv, 2330) and altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone (TrMv, 5280), un
TrMv
Complexly deformed assemblage of altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone, Angayucham-Tozitna terrane
Composed of a wide variety of mafic and intermediate volcanic and intrusive rocks including basalt, and andesite, diabase, gabbro, and volcaniclastic rocks that are weakly metamorphosed to prehnite-pumpellyite and locally to greenshist facies assemblages
Triassic to Mississippian
Locally abundant fossil occurrences
Complexly deformed assemblage of altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone
Angayucham-Tozitna terrane
Composed of a wide variety of mafic and intermediate volcanic and intrusive rocks including basalt, and andesite, diabase, gabbro, and volcaniclastic rocks that are weakly metamorphosed to prehnite-pumpellyite and locally to gr
MzPzb
Altered basalt, diabase, and subordinate limestone
Dominantly dark-green to gray altered basalt and fine-grained diabase, containing subordinate cherty tuff and pods of recrystallized limestone.
early Mesozoic and Paleozoic
Unidentifiable crinoid stem fragments in limestone pod
ls
Limestone
Scattered limestone bodies within unit TrMv
Locally abundant fossil occurances
Limestone pods in altered basalt, diabase, and subordinate limestone
Recrystallized limestone in unit MzPzb, consisting of dominantly dark-green to gray altered basalt and fine-grained diabase, containing subordinate cherty tuff and pods of recrystallized limestone.  Correlation highly tentative with unit MDl of Innoko se
KCgg
Gemuk Group (altered mafic volcanics and sedimentary rocks)
Mafic volcanic rocks altered to gneissoid and schistose rocks in some areas.  Light grreenish gray tuff with interbedded siltstone, overlain by volcanic agglomerate, impure limestone, graywacke, and chert
Cretaceous to Carboniferous?
Hornfels.  Brown to gray, massive to locally porphyroblastic chlorite-biotite hornfels, partly tourmaline rich
Formed in the ternal aureole bordering the granitic cores of the Fox Hills and Russian Mountains.  Consists of metasitlstone, metasandstone, metaconglomerate and subordinate amounts of metavolcanic rocks