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 Detterman, R.L., and Reed, B.L., 1973, Surficial deposits of the Iliamna quadrangle, Alaska: U.S. Geological Survey Bulletin 1368-A, 64 p., 1 plate, scale 1:250,000.
Symbol Qgl
Unit name Proglacial lake deposits
Description These deposits are almost entirely silt- and clay-size, though locally sand and pebbles occur near ground moraine exposures. Silt and clay is light-gray to tan, locally laminated and as much as 20-50 feet thick. Upper layers are rich in organic material. Lenses of interstitial ice are present and relict permafrost (Periglacial) features are common. Proglacial lake deposits have a characteristic topographic expression, nearly flat and covered by myriad small ponds, remnants of larger ponds and the intervening areas covered by quaking bogs.
Lithology Unconsolidated

Correlated geologic units

Label Qgl
Description Glaciolacustrine deposits
Geologic age Pleistocene to Holocene
Geologic setting Unconsolidated
Lithology Form Importance
Sand < Coarse-detrital < Unconsolidated Lacustrine Major
Silt < Fine-detrital < Unconsolidated Lacustrine Major
Clay < Fine-detrital < Unconsolidated Lacustrine Indeterminate, major