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 Qbo
Unit name Brooks Lake outwash plains, kame terrace and pitted outwash deposits
Description Glaciofluvial deposits bordering moraine fronts of the Kvichak and Iliamna advances, commonly 1.5 to 2 miles wide and many miles long. Thought to be so extensive because of protracted stillstands of the glacial advances.Deposits form great plains, dipping 25 to 50 feet per miles and showing shallow braided channels scars due to rapidly shifting streams. Pitted outwash border the moraines where outwash cover ice blocks and ultimately melted out, leaving depressions as much as 50 feet deep. At west end of Iliamna lake, outwash is 65 feet thick, composed of alternating layers of silt and gravel and containing lenses of cobbles. A well-developed kame terrace extends along south side of Kvichak moraine west from Kukaklek Lake. It is 300 to 800 feet wide and the inner (ice) margin is a scrap 25-50 feet high. Outwash locally mantles morainal deposits of the Mak Hill and older Brooks Lake advances
Lithology Unconsolidated

Correlated geologic units

Label Qwo
Description Outwash deposits, late Wisconsin-age Glaciations
Geologic age Late-Pleistocene
Geologic setting Unconsolidated
Lithology Form Importance
Sand < Coarse-detrital < Unconsolidated Glacial, outwash Major
Gravel < Coarse-detrital < Unconsolidated Glacial, outwash Indeterminate, major
Silt < Fine-detrital < Unconsolidated Glacial, outwash Minor