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 Wilson, F.H., Detterman, R.L., and DuBois, G.D., 2015, Geologic framework of the Alaska Peninsula, southwest Alaska, and the Alaska Peninsula terrane: U.S. Geological Survey Bulletin 1969-B, scale 1:500,000, 2 plates, 34 p.
Symbol Qa
Unit name Alluvial deposits
Description Ranges from coarse, subangular rock fragments to fine sand and silt in grain size; locally includes considerable amounts of pumice near volcanic centers. As mapped, unit locally incorporates deposits of fluvial, colluvial, glacial outwash, lacustrine, estuarine, swamp, and eolian origin, in addition to minor areas of other Quaternary surficial units. Large areas are covered by organic-rich silt deposits. Unit includes much volcanic ash and volcanic debris in vicinity of Katmai, Aniakchak, Kametolook, and Joshua Green Rivers, Knife Creek, and unnamed river west of Kametolook River, as well as in vicinity of most volcanoes, particularly those of Pavlof group and on Unimak Island. Eolian deposits form dunes 10 to 20 m high that are composed largely of sand and pumice
Lithology Unconsolidated

Correlated geologic units

Label Qa
Description Alluvium
Geologic age Pleistocene to Holocene
Geologic setting Unconsolidated
Lithology Form Importance
Gravel < Coarse-detrital < Unconsolidated Bed Major
Sand < Coarse-detrital < Unconsolidated Bed Major
Coarse-detrital < Unconsolidated Bed Indeterminate, major
Silt < Fine-detrital < Unconsolidated Bed Indeterminate, major
Peat < Unconsolidated Bed Indeterminate, major