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 Qbil
Unit name Brooks Lake drift, Iliamna Stade
Description Little modified, showing fresher knob-and-kettle topography than Kvichak moraines. Contains a heterogeneous assemblage of rock types indicating multiple sources of tributary glaciers. Ice-polished and striated erratics are common on surface of the moraines. Well-preserved lobate end moraines can be followed for many miles; recessional moraines are less preserved, being partially covered by glaciofluvial deposits. Kettle ponds are for most part undrained and retain the irregular shapes left by melting ice blocks, locally loess and vegetation are infilling the kettles. Some of the youngest moraines are locally heavily forested, whereas the oldest moraines at comparable elevations may be only tundra covered. These end moraines lie 20 to 60 miles beyond the Newhalen end moraines and a complex system of recessional moraines indicate at least three major stillstands
Lithology Unconsolidated

Correlated geologic units

Label Qw1
Description Late Wisconsin, Iliamna and other till
Geologic age Late-Pleistocene
Geologic setting Unconsolidated
Lithology Form Importance
Gravel < Coarse-detrital < Unconsolidated Glacial Major
Boulders < Coarse-detrital < Unconsolidated Glacial Indeterminate, major
Sand < Coarse-detrital < Unconsolidated Glacial Indeterminate, major
Silt < Fine-detrital < Unconsolidated Glacial Indeterminate, major