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 Qdf
Unit name Brooks Lake hanging delta and outwash fan deposits
Description Deposits of gravel, sand and silt, these are the result of streams draining into ancestral Lake Iliamna. Typically deltaic and consist of stratified layers of cobbles, pebbles, sand, silt, and glacial lake clay. Mostly associated with outwash of the Kvichak and Iliamna stades. Are at two levels, coarser ones are at the higher level, generally above 200 feet and larger, being 2 to 4 miles long and as wide in a triangular shape. Deltas of lower set are commonly narrow and more linear, up to 4 miles long and and rarely more than 1/4 to 1/2 mile wide; these tend to be 100 to 150 feet in elevation and most sand and silt
Lithology Unconsolidated

Correlated geologic units

Label Qglf
Description Glacial outwash derived fans deposited in ephermeral glacial lakes
Geologic age Pleistocene
Geologic setting Unconsolidated
Lithology Form Importance
Sand < Coarse-detrital < Unconsolidated Lacustrine Major
Gravel < Coarse-detrital < Unconsolidated Lacustrine Indeterminate, major
Silt < Fine-detrital < Unconsolidated Lacustrine Indeterminate, major