NSACLASS,LABEL,NAME,AGE,DESCRIPTION,SYMBOL,OVERPRINT,SOURCES
100,Qac,"Alluvial, coluvial, and glacial drift deposits, undivided",Quaternary,"Alluvial and colluvial deposits consist mainly of silt, sandy silt, and peat. Alluvium is chiefly fluvial in origin, but locally includes reworked windblown deposits. Alluvium deposits cover wide areas of the Yukon and Kuskokwim lowlands and delta plain. Colluvial deposits make up the bulk of the unconsolidated deposits on the uplands slopes. Colluvium includes glacial drift composed of sand, gravel, and boulder morainal and outwash deposits.  Glacial drift is found at higher elevations in the Russian and Kilbuck Mountains in the Russian Mission quadrangle and in the Askinuk Mountains in the Hooper Bay quadrangle.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
105,Qf,"Floodplain, tidal flats, and estuarine deposits",Quaternary,"Unit composed chiefly of silt, fine sand, and peat. Some gravel and coarse sand deposits occur locally along the tributary streams draining upland areas.  The tidal flats and estuarine deposits consist of fluvial silt and sandy silt that have been reworked and redeposited by brackish-water tidal currents.  Deposits form broad swaths along the Yukon and Kuskokwim Rivers and their major tributaries and include tidal flats and estuarine deposits along the shores of the Bering Sea and Norton Sound.  The floodplain deposits are characterized physiographically by bars, oxbow lakes, meander scrolls, abandoned channels, and other evidence of recent floodplain building.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
115,Qbl,Beach and lagoonal deposits,Quaternary,"Silt and sandy silt.  Unit includes active offshore bars, spits, and beaches ridges and former beach ridges that have been recently stabilized by a thin vegetation cover. Scattered localities along the Norton Sound and Bering Sea coast in the St. Michael, Kwiguk, Black, and Hooper Bay quadrangles.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
120,Qw,Wind-blown deposits,Quaternary,Silt and sandy silt deposits form broad partly dissected stabilized dune fields in the lowlands of the Yukon and Kuskokwim Rivers.  They compose sheet-like bodies as much as 100 feet thick that are characterized by modified dunes and blowouts.  The dune fields overlie the alluvial and colluvial deposits of unit Qac and predate the floodplain deposits of unit Qf.,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
330,Qb,Young scoriaceous tholeiitic basalt lava flows and cones,Quaternary,Young scoriaceous tholeiitic basalt lava flows and cones. Mapped separately on the western half of Stuart Island in the St Michael quadrangle.  The flows and cones are unmodified by erosion suggesting a Holocene or late Pleistocene age,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
350,QTb,Basalt lava flows,Quaternary  and latest Tertiary,"Vesicular tholeiitic and alkali basalt lava flows, cones and maar craters.  The flows are interlayered with thinner pyroclastic deposits that range from fine ash to coarse breccia.  The lava flows are overlain locally by younger cinder cones and short flows, which have little or no vegetation cover.  Unit is exposed chiefly in the St. Michael quadrangle where it forms the western end of a broad volcanic field that extends eastward into the adjoining Unalakleet quadrangle.  Smaller volcanic fields belonging to this unit also are present on the delta plain in the Marshall, Kwiguk, and Hooper Bay quadrangles.  Samples collected from the volcanic field in the adjoining Unalakleet quadrangle yield whole-rock K-Ar ages ranging from 3.25Ma to 0.19 Ma (Patton and Moll-Stalcup, 1996).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1004,Tb,Basalt lava flows,late Tertiary,Flat-lying vesicular basalt yielding whole-rock K/Ar ages of 19.35 Ma and 6.19 Ma (table 1).  Basalt flows located in Three small areas in the Russian Mission quadrangle: two on the Yukon River in the northwestern part of the quadrangle and one on the Owhat River in the northeastern part of the Russian Mission quadrangle.,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1600,TKad,"Dacite, rhyolite, andesite, and basalt lava flows, and volcaniclastic and hypabyssal rocks, undivided",Tertiary and latest Cretaceous,"Dacite, rhyolite, andesite, and basalt lava flows, and volcaniclastic and hypabyssal rocks, undivided. Confined to the Holy Cross quadrangle and northern part of the Russian Mission quadrangle where field data are insufficient to map units TKa and TKd separately.   May locally include basalt lava flows as young as late Tertiary  (unit Tb). Two samples, one from a rhyolite flow, and the other from a devitrified  tuff, yielded sanidine isotopic K/Ar ages of 67.0 Ma and 64.7 Ma (table 1). Both samples are from an area mapped as unit TKad, an undivided assemblage of dacite, rhyolite, andesite, and basalt flows, and volcaniclastic and hypabyssal rocks in the northeastern corner of the Holy Cross quadrangle.TKhf - Hornfels altered equivalent - Metasiltstone, metasandstone, metaconglomerate and subordinate amounts of metavolcanic rocks formed in the thermal aureole bordering the granitic cores of the Fox Hills, in the southeastern part of the Holy Cross quadrangle, and the Russian Mountains, in the northeastern part of the Russian Mission quadrangle.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1601,TKi,Shallow intrusive rocks of intermediate and silicic composition,early Tertiary and latest Cretaceous,"Rhyolite, dacite and lesser amounts of trachyte and andesite. Typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende.  Unit forms numerous large sills, dikes, and domes intruding Cretaceous sedimentary rocks in the northwestern Holy Cross quadrangle, in the northeastern Kwiguk quadrangle, and in the Kusilvak Mountains in the southwestern part of the Kwiguk quadrangle.  A felsic to intermediate dike in the southern part of the Holy Cross quadrangle has a Pb/U zircon age of 63.6 Ma and a 40Ar/39Ar age of 67.3 Ma.  A dike of similar composition from the same general region has a 40Ar/39Ar age of 60.4 Ma (table 1). Elsewhere the unit occurs as small isolated bodies most of which are too small to be shown separately on the map.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1602,TKi,Shallow intrusive rocks of intermediate and silicic composition,early Tertiary and latest Cretaceous,"Rhyolite, dacite and lesser amounts of trachyte and andesite. Typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende.  Unit forms numerous large sills, dikes, and domes intruding Cretaceous sedimentary rocks in the northwestern Holy Cross quadrangle, in the northeastern Kwiguk quadrangle, and in the Kusilvak Mountains in the southwestern part of the Kwiguk quadrangle.  A felsic to intermediate dike in the southern part of the Holy Cross quadrangle has a Pb/U zircon age of 63.6 Ma and a 40Ar/39Ar age of 67.3 Ma.  A dike of similar composition from the same general region has a 40Ar/39Ar age of 60.4 Ma (table 1). Elsewhere the unit occurs as small isolated bodies most of which are too small to be shown separately on the map.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1603,TKd,"Dacite and rhyolite lows, domes, ash-flow tuffs, and hypabyssal rocks",early Teritiary and latest Cretaceous,"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 felsic groundmass. Unit forms a large volcanic field in the southeastern part of the Holy Cross quadrangle and is widely distributed elsewhere in the Holy Cross and Russian Mission quadrangles as small bodies that intrude or are interlayered with andesite and basalt belonging to unit TKa.  Most of these bodies are too small or too poorly known to be mapped separately.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1605,TKa,Andesite and basalt flows and volcanicclasitc rocks,early Tertiary and latest Cretaceous,"Andesite and basalt lava flows and volcaniclastic rocks widely exposed in the central part of the Holy Cross quadrangle and in a small area in the north-central part of the Russian Mission quadrangle between the Yukon and Kuskokwim Rivers. Flows are generally porphyritic and composed of phenocrysts of plagioclase and pyroxene in a groundmass of plagioclase microlites.  Some of the flows are columnar jointed and locally vesicular.  Volcaniclastic rocks in this unit include breccia, tuffs, and agglomerates.  The andesitic and basaltic rocks commonly are interlayered with or intruded by small bodies of dacite and rhyolite belonging to units TKi and TKd.  Two basalt samples from outcrops on the Yukon River near the northern edge of the map area yield K/Ar isotopic ages of 50.8 and 42.9 Ma (table 1).  No other age data are available from the map area, but in the adjoining Unalakleet quadrangle to the north similar basaltic rocks yield five K/Ar isotopic ages that range from 65.2 to 51.9 Ma (Patton and Moll-Stalcup, 1996).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1620,TKi,Shallow intrusive rocks of intermediate and silicic composition,early Tertiary and latest Cretaceous,"Rhyolite, dacite and lesser amounts of trachyte and andesite. Typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende.  Unit forms numerous large sills, dikes, and domes intruding Cretaceous sedimentary rocks in the northwestern Holy Cross quadrangle, in the northeastern Kwiguk quadrangle, and in the Kusilvak Mountains in the southwestern part of the Kwiguk quadrangle.  A felsic to intermediate dike in the southern part of the Holy Cross quadrangle has a Pb/U zircon age of 63.6 Ma and a 40Ar/39Ar age of 67.3 Ma.  A dike of similar composition from the same general region has a 40Ar/39Ar age of 60.4 Ma (table 1). Elsewhere the unit occurs as small isolated bodies most of which are too small to be shown separately on the map.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1625,TKd,"Dacite and rhyolite lows, domes, ash-flow tuffs, and hypabyssal rocks",early Teritiary and latest Cretaceous,"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 felsic groundmass. Unit forms a large volcanic field in the southeastern part of the Holy Cross quadrangle and is widely distributed elsewhere in the Holy Cross and Russian Mission quadrangles as small bodies that intrude or are interlayered with andesite and basalt belonging to unit TKa.  Most of these bodies are too small or too poorly known to be mapped separately.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1635,TKa,Andesite and basalt flows and volcanicclasitc rocks,early Tertiary and latest Cretaceous,"Andesite and basalt lava flows and volcaniclastic rocks widely exposed in the central part of the Holy Cross quadrangle and in a small area in the north-central part of the Russian Mission quadrangle between the Yukon and Kuskokwim Rivers. Flows are generally porphyritic and composed of phenocrysts of plagioclase and pyroxene in a groundmass of plagioclase microlites.  Some of the flows are columnar jointed and locally vesicular.  Volcaniclastic rocks in this unit include breccia, tuffs, and agglomerates.  The andesitic and basaltic rocks commonly are interlayered with or intruded by small bodies of dacite and rhyolite belonging to units TKi and TKd.  Two basalt samples from outcrops on the Yukon River near the northern edge of the map area yield K/Ar isotopic ages of 50.8 and 42.9 Ma (table 1).  No other age data are available from the map area, but in the adjoining Unalakleet quadrangle to the north similar basaltic rocks yield five K/Ar isotopic ages that range from 65.2 to 51.9 Ma (Patton and Moll-Stalcup, 1996).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1650,TKi,Shallow intrusive rocks of intermediate and silicic composition,early Tertiary and latest Cretaceous,"Rhyolite, dacite and lesser amounts of trachyte and andesite. Typical rock is composed of a fine-grained felsic groundmass with phenocrysts of plagioclase, quartz, biotite, and hornblende.  Unit forms numerous large sills, dikes, and domes intruding Cretaceous sedimentary rocks in the northwestern Holy Cross quadrangle, in the northeastern Kwiguk quadrangle, and in the Kusilvak Mountains in the southwestern part of the Kwiguk quadrangle.  A felsic to intermediate dike in the southern part of the Holy Cross quadrangle has a Pb/U zircon age of 63.6 Ma and a 40Ar/39Ar age of 67.3 Ma.  A dike of similar composition from the same general region has a 40Ar/39Ar age of 60.4 Ma (table 1). Elsewhere the unit occurs as small isolated bodies most of which are too small to be shown separately on the map.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1655,TKg,"Granite, granodiorite, syenite, and monzonite",early Tertiary and latest Cretaceous,"Unit is composed of plutonic rocks that have been assigned various petrographic names based largely on field inspection and examination of only a few thin sections.  The most common rock type appears to be biotite granite, but other rock types include granodiorite, quartz diorite, syenite , quartz monzonite, monzonite, monzodiorite, and diorite. Unit forms the core of a domal volcano-plutonic complex in the Russian Mountains in the northeastern part of the Russian Mission quadrangle and a similar domal complex in the Fox Hills in the southeastern part of the Holy Cross quadrangle.  Unit also composes two large plutonic bodies and a number of small stocks in the northwestern part of the Russian Mission quadrangle and one small stock in the Kilbuck Mountains at the southern edge of the Russian Mission quadrangle. The only detailed chemical data come from the domal complex in the Russian Mountains, which according to Bundtzen and Laird, (1991) is composed of an outer rim of syenite, monzonite, and quartz monzonite and a core of quartz syenite and porphyritic quartz monzonite. A large pluton located in the northwest corner of the Russian Mission quadrangle and extending into the eastern edge of the Marshall quadrangle locally displays a strong gneissic banding.  Seven K/Ar cooling ages from this unit range from 70.9 to 60.9 Ma (table 1).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1682,TJm,Altered mafic plutonic rocks,early Tertiary? to Jurassic?,"Altered gabbro and diorite bodies crops out as small scattered bodies in the Russian Mission and southern Holy Cross quadrangles. Intrudes units Jab, Jvc, KJv, and KMu. Age of unit is uncertain, but not older than Jurassic.  Some or the entire unit may be as young as Tertiary.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1943,Kym,"Yukon-Koyukuk Basin, marginal shelf and slope deposits, polymict conglomerate, sandstone, siltstone, and shale",Cretaceous,"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-washed quartz-rich sandstone. Unit poorly exposed along the eastern and western margins of the Yukon-Koyukuk Basin. On the eastern margin unit crops out at scattered localities in the southern Holy Cross and northern Russian Mission quadrangles. Some conglomerate beds on the eastern margin contain abundant granitic rock clasts.  On the western margin exposures of this unit are confined to a few small isolated outcrops on the coastal plain in the northern Kwiguk and the southeastern St. Michael quadrangles. Well-preserved leaf impressions of Cretaceous (Albian-Cenomanian?) age occur in shale beds and along the eastern margin of the basin in the Holy Cross quadrangle (table 2).TKhf - Hornfels altered equivalent - Metasiltstone, metasandstone, metaconglomerate and subordinate amounts of metavolcanic rocks formed in the thermal aureole bordering the granitic cores of the Fox Hills, in the southeastern part of the Holy Cross quadrangle, and the Russian Mountains, in the northeastern part of the Russian Mission quadrangle.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
1985,Kks,"Kuskokwim Basin, deltaic and submarine fan deposits, undivided, sandstone, siltstone, and shale",Cretaceous,"Deltaic and submarine fan deposits. The deltaic deposits consist of well-sorted, quartz-rich, cross-bedded sandstone interbedded with siltstone and shale.  The submarine fan deposits are composed of turbiditic sequences that grade from fine- to medium-grained graywacke to laminated mudstone. Exposures of this unit are confined to the eastern margin of the map area in the northeastern Russian Mission quadrangle and adjoining parts of the Holy Cross quadrangle and in the Kilbuck Mountains in the southeastern Russian Mission quadrangle.  These deposits form the western margin of the Kuskokwim Basin, a broad Cretaceous sedimentary trough that extends from central Alaska nearly to Bristol Bay. Marine mollusks collected from this unit in the Russian Mission quadrangle are of Late Cretaceous (Cenomanian-Turonian) age (table 2).TKhf - Hornfels altered equivalent - Metasiltstone, metasandstone, metaconglomerate and subordinate amounts of metavolcanic rocks formed in the thermal aureole bordering the granitic cores of the Fox Hills, in the southeastern part of the Holy Cross quadrangle, and the Russian Mountains, in the northeastern part of the Russian Mission quadrangle.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2021,KJv,"Koyukuk Terrane, Andesitic and basaltic volcaniclastic rocks and lava flows, chert, and mudstone",Early Cretaceous and Jurassic,"Highly disrupted assemblage of mafic to intermediate tuff, breccia, agglomerate, volcanic-rich conglomerate and graywacke, cherty tuff, chert, mudstone, and andesitic and basaltic pillow lava.  Unit locally intruded by sills and dikes of diabase, diorite, and gabbro. Tuffs commonly are laumontitized. Some of the conglomerate beds east of the Yukon River in the Holy Cross quadrangle contain clasts of altered granitic rocks.  Unit crops out in localities scattered in the Holy Cross quadrangle and the northern part of the Russian Mission quadrangle.  Unit also includes several small exposures along the faulted western boundary of the Yukon-Koyukuk basin in the Kwiguk quadrangle and in the adjoining St Michael quadrangle. Unit is assigned an Early Cretaceous to Jurassic age based on sparse isotopic and fossil data and on its stratigraphic position below the late Early Cretaceous sedimentary rocks of the Yukon-Koyukuk basin and above the Triassic rocks of the Angayucham-Tozitna terrane.  In the area east of the Yukon River a diorite intrusive body in this unit yielded a K/Ar amphibole cooling age of 128 Ma (Early Cretaceous) and an andesite porphyry clast from a volcanic conglomerate gave a K/Ar amphibole age of 164 Ma (Middle Jurassic).  In the area  east of the Yukon River a diorite intrusive body in this unit yielded an amphibole K/Ar amphibole cooling age of 128 Ma (Early Cretaceous) and an andesite porphyry clast from a volcanic conglomerate gave a K/Ar amphibole age of 164 Ma (Middle Jurassic)  (table 1). On Yukon River in the western part of the Russian Mission quadrangle, thin beds of calcareous tuffs contain mollusks of Early Cretaceous (Hauterivian and Valanginian) age (table 2).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2021,Kys,"Yukon-Koyukuk Basin, Deltaic Deposits, sandstone and siltstone",Cretaceous,"Fluvial and shallow marine deltaic deposits of sandstone, siltstone, and shale.  Locally crossbedded and ripple marked.  Unit contains abundant plant debris and fresh- and brackish-water mollusks. Unit is widely exposed in a broad belt that extends from the northwestern Holy Cross quadrangle through the eastern Kwiguk quadrangle and into the northern edge of the Marshall quadrangle. A few scattered exposures also occur in the southeastern part of Holy Cross quadrangle. Shallow water marine mollusks of mid-Cretaceous age found in the Kwiguk quadrangle (table 2).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2023,Kys,Dot pattern where Kys is intruded by numerous small hypabyssal bodies of rhyolite and dacite (TKi),Cretaceous,"Undivided areas where numerous small hypabyssal bodies of rhyolite and dacite (TKi) intrude the Kys unit.  Kys-fluvial and shallow marine deltaic deposits of sandstone, siltstone, and shale.  Locally crossbedded and ripple marked.  Unit contains abundant plant debris and fresh- and brackish-water mollusks. Unit is widely exposed in a broad belt that extends from the northwestern Holy Cross quadrangle through the eastern Kwiguk quadrangle and into the northern edge of the Marshall quadrangle. A few scattered exposures also occur in the southeastern part of Holy Cross quadrangle. Shallow water marine mollusks of mid-Cretaceous age found in the Kwiguk quadrangle (table 2).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2102,Kygc,"Yukon-Koyukuk Basin, submarine fan deposits, highly calcareous graywacke sandstone and mudstone turbidites",Cretaceous,"Turbidites composed of highly calcareous sandstone interbedded with noncalcareous micaeous siltstone and shale. Unit is infolded with and locally intertongues with unit Kygv. Unit extends in a broad belt from the southeast corner of St. Michael quadrangle and the northwest corner of the Holy Cross quadrangle to the south-central part of the Kwiguk quadrangle. No fossils found in this unit, but elsewhere in the Yukon-Koyukuk Basin similar assemblages have yielded marine mollusks of probable late Early or early Late Cretaceous age (Patton, Wilson, Labay, and Shew, 2006).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2105,Kygv,"Yukon-Koyukuk Basin, submarine fan deposits, graywacke sandstone and mudstone turbidites containing abundant laumontitized volcanic debris",Cretaceous,"Hard, well-indurated, fine- to medium-grained, locally tuffaceous, sandstone and micaceous mudstone.  Some sandstone beds have a distinctly mottled appearance owing to the presence of laumontite, most commonly in tuffaceous-rich layers. Unit widely exposed in a broad belt extending from the southeastern corner of the St. Michael quadrangle to the south-central part of the Kwiguk quadrangle. Unit is infolded with and locally intertongues with unit Kygc. No fossils reported in the map area, but elsewhere in the Yukon-Koyukuk basin, a lithologically similar unit has yielded marine mollusks of late Early Cretaceous age (Patton, Wilson, Labay, and Shew, in press).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2180,Kyg,"Yukon-Koyukuk Basin, submarine fan deposits, graywacke sandstone and mudstone turbidites, undivided",Cretaceous,Sparse field data on this sedimentary rock unit suggests that this unit is composed largely of graywacke turbidites including both highly calcareous graywacke as in unit Kygc and graywacke containing abundant volcanic debris as in unit Kygv. Unit poorly exposed along the eastern margin of the Yukon River delta plain in the southeastern part of the St. Michael quadrangle and in the adjoining Kwiguk quadrangle. Unit also crops out in the Kusilvak Mountains in the southwestern part of the Kwiguk quadrangle and in the adjoining Marshall quadrangle.,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2400,Kg,Granodiorite and granite,Late and Early Cretaceous,Biotite granite and hornblende-biotite granodiorite forming two large plutons that intrude the Nyac terrane in Kilbuck Mountains of the southern Russian Mission quadrangle and a large pluton that forms the Askinuk Mountains in the Hooper Bay quadrangle.  Samples from plutons in the Kilbuck Mountains processed for isotopic ages yielded K/Ar and 40Ar39Ar cooling ages ranging from 101 to 120Ma and U/Pb zircon crystallization age of between 104 and 129 Ma (upper Concordia intercept).  A single sample from the Askinuk Mountains pluton yielded a biotite K/Ar cooling age of 80.6ñ4.0 Ma (table 1).,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2410,Kg,Granodiorite and granite,Late and Early Cretaceous,Biotite granite and hornblende-biotite granodiorite forming two large plutons that intrude the Nyac terrane in Kilbuck Mountains of the southern Russian Mission quadrangle and a large pluton that forms the Askinuk Mountains in the Hooper Bay quadrangle.  Samples from plutons in the Kilbuck Mountains processed for isotopic ages yielded K/Ar and 40Ar39Ar cooling ages ranging from 101 to 120Ma and U/Pb zircon crystallization age of between 104 and 129 Ma (upper Concordia intercept).  A single sample from the Askinuk Mountains pluton yielded a biotite K/Ar cooling age of 80.6ñ4.0 Ma (table 1).,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2480,Kg,Granodiorite and granite,Late and Early Cretaceous,Biotite granite and hornblende-biotite granodiorite forming two large plutons that intrude the Nyac terrane in Kilbuck Mountains of the southern Russian Mission quadrangle and a large pluton that forms the Askinuk Mountains in the Hooper Bay quadrangle.  Samples from plutons in the Kilbuck Mountains processed for isotopic ages yielded K/Ar and 40Ar39Ar cooling ages ranging from 101 to 120Ma and U/Pb zircon crystallization age of between 104 and 129 Ma (upper Concordia intercept).  A single sample from the Askinuk Mountains pluton yielded a biotite K/Ar cooling age of 80.6ñ4.0 Ma (table 1).,,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2870,KJb,"Nyak Terrane, Basalt and andesite lava flows",Early Cretaceous and/or Late Jurassic,"Variably altered basalt and andesite.  Conformably(?) overlies unit Jab and unconformably(?) overlain by unit TJb. Unit confined to Kilbuck Mountains, southeastern Russian Mission quadrangle. Assigned an Early Cretaceous to latest Jurassic age.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2870,TJb,Whitefish Lake Volcanic Field,early Tertiary? to Jurassic?,"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. Unit confined to Kilbuck Mountains, southeastern Russian Mission quadrangle. Regional relationships suggest unit could be as old as Jurassic or as young as Tertiary.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
2885,TJi,Hyabyssal felsic intrusive rocks,early Tertiary? to Jurassic?,"Altered rhyolite and dacite porphyries confined to a single body in the Kilbuck Mountains, southeastern Russian Mission quadrangle. Age of unit is uncertain, but not older than Jurassic.  May be as young as Tertiary.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
3120,Jvc,"Nyak Terrane, volcaniclastic conglomerate, sandstone, and shale",Late and Middle Jurassic,"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. Mollusks  collected from this unit  are of Late Jurassic (late Kimmeridgian to early Tithonian) age (table 2).  Middle Jurassic (Bajocian) mollusks are reported by Box and others (1993) from this unit in the adjoining Bethel quadrangle south of the Russian Mission quadrangle.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
3380,Jt,"Koyukuk Terrane, Trondhjemite, tonalite, and gabbro",Jurassic,"Unit is composed chiefly of trondjhemite and tonalite plutonic bodies that locally have been metasomatized by potassium-rich fluids to a pink granite and granonodiorite.  Unit also includes subordinate amounts of quartz diorite, diorite, and gabbro.  Some of the plutonic bodies have been cataclastically deformed. Unit confined to the north-central part of the Holy Cross quadrangle where it intrudes a fault-bounded belt of undivided Koyukuk and Angayucham-Tozitna terranes (KMu). Unit is assigned a Jurassic age based on data from the adjoining Unalakleet quadrangle where similar plutonic bodies yield K/Ar isotopic cooling ages that range from 173 to 130 Ma (Patton and Moll-Stalcup, 1996).",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
3450,Jab,"Nyak Terrane, andesitic and basaltic lava flows and marine volcaniclastic rocks",Middle Jurassic,"Andesitic and basaltic lava flows and flow breccias.  Tuffaceous sandstone and conglomerate containing abundant clasts of mafic and intermediate volcanic and intrusive rocks.  Unit altered to low-grade metamorphic facies by variable replacement of primary minerals by chlorite, calcite, epidote, albite, and quartz. Unit confined to Kilbuck Mountains, southeastern Russian Mission quadrangle. Unit assigned a Middle Jurassic (Bajocian) age based on the presence of marine mollusks.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
3498,MzPzum,"Koyukuk Terrane, serpentinized ulramafic rocks",Mesozoic and Paleozoic?,"Unit presumed to be composed of partly serpentinized harzburgbite and dunite.  May also include some gabbro. Unit confined to four small bodies distributed along the eastern side of a fault-bounded belt composed of units KMu and Jt in the north-central part of the Holy Cross quadrangle.  Although the four bodies were mapped entirely by aerial reconnaissance, their appearance and erosional characteristics are similar to small bodies of ultramafic rocks which were mapped on the ground a short distance to the north in the Unalakleet quadrangle (Patton and Moll-Stalcup, 1996). Unit probably Mesozoic in age, but may be as old as Paleozoic.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
5235,KMu,"Angayucham-Tozitna Terrane, 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,"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.",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."
5280,TrMv,"Angayucham-Tozitna Terrane, complexly deformed assemblage of altered basalt, chert, chert breccia, argillite, tuff, volcaniclastic graywacke, and limestone",Triassic to Mississippian,"Unit composed of a wide variety of mafic and intermediate volcanic and intrusive rocks including basalt, andesite, diabase, gabbro, and volcaniclastic rocks that are weakly metamorphosed to prehnite-pumpellyite and locally to greenschist facies assemblages.  The volcanic and intrusive rocks are interbedded with varicolored radiolarian chert, chert breccia, chert pebble conglomerate, argillite, graywacke, and small limestone bodies.  The chert, argillite, graywacke, and limestone are locally metamorphosed to metachert, slate, pelitic schist and marble.  Unit assigned a Triassic to Mississipian age based on locally abundant fossils, chiefly from scattered limestone bodies in southwestern Holy Cross and northwestern Russian Mission quadrangles (table 2).  A small body of amphibolite from near the northwestern border of the Russian Mission quadrangle yielded a K/Ar isotopic cooling age of 349.27ñ10.48 Ma (early Mississippian) (table 1)",,,"Patton, W.W., Jr., Wilson, F.H., and Labay, K.A. , in prep.,  Reconnaissance geologic map of  the lower Yukon River Region, Alaska:  U.S. Geological survey Scientific Investigations Serives Map SIM-xxxxx, scale 1:500,000."