Unconsolidated surficial deposits, undivided

Unit symbol: Qs
Age range Quaternary (1.806 to 0 Ma)
Lithology: Unconsolidated
Group name: Unconsolidated and poorly consolidated surficial deposits
Unconsolidated, poorly to well-sorted, poorly to moderately well-stratified deposits; consist predominantly of alluvial, colluvial, marine, lacustrine, eolian, and swamp deposits. May include some glacial deposits. Also includes widespread glacial and periglacial deposits that consist of end, lateral, and ground moraine, outwash, rock glacier deposits, and other glacial and periglacial deposits as well as glacially scoured bedrock that may be covered with thin, glacially derived deposits. These glacial deposits are of Holocene and Pleistocene age and may include small areas of potentially latest Tertiary deposits. Map unit locally includes reworked volcanic debris as well as block and ash flows. On generalized map, shown as part of unit QTs

Source map information

Source map Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic map of the eastern half of the McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14a, 34 p., 1 sheet, scale 1:125,000.
Symbol Qat
Unit name Terrace Alluvium
Description Moderately to well sorted, well stratified, gray to tan (oxidized), fluvial silt, sand, and gravel of varying ages deposited on former floodplains that now lie above or beyond the normal depositional regime of Holocene streams.
Lithology Unconsolidated

Correlated geologic units

Label Qt
Description Terrace deposits
Geologic age Pleistocene to Holocene
Geologic setting Unconsolidated
Lithology Form Importance
Gravel < Coarse-detrital < Unconsolidated Alluvial Major
Sand < Coarse-detrital < Unconsolidated Terrace, stream Major
Silt < Fine-detrital < Unconsolidated Terrace, stream Major
Boulders < Coarse-detrital < Unconsolidated Terrace, stream Indeterminate, major