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GEOLOGIC AND STRUCTURE CONTOUR MAP OF THE - page 5 / 10

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DESCRIPTION OF MAP UNITS SIDNEY 30´ x 60´ QUADRANGLE

Note: Thicknesses are given in feet because original base maps used feet. To convert feet to meters (the contour interval unit on this map), multiply feet x 0.3048.

Qal

Alluvium (Holocene)—Light-brown, yellowish-brown, grayish-brown, brown, olive, gray, and light-gray gravel, sand, silt, and clay deposited in stream and river channels and on flood plains. Gravel clasts poorly to well sorted and as much as 2 ft in diameter. Deposits poorly to well stratified. Thickness generally less than 20 ft, but locally as much as 40 ft.

Qgr

Gravel (Holocene and Pleistocene?)—Alluvium and colluvium reworked directly from QTat deposits and deposited on slopes. Color and composition identical to uncemented QTat. Thickness less than 20 ft.

Qac

Alluvium and colluvium, undivided (Holocene)—Dominantly sand, silt, and clay in glacial meltwater channels. Color reflects that of older Quaternary and Tertiary units from which it was derived. May locally overlie glacial outwash deposits. Thickness not determined.

Qat

Alluvial terrace deposit (Holocene and Pleistocene)—Light-brown, grayish- brown, and light-gray gravel, sand, and silt in terrace remnants at elevations ranging from 5 to 360 ft above modern rivers and streams. Gravel clasts generally well sorted and dominantly well rounded. Deposits poorly to well stratified. Thickness generally less than 20 ft.

Qgt

Glacial till (Pleistocene)—Heterogeneous mixture of light-brown, grayish- brown, and light-gray clay, silt, sand, and gravel with rare to abundant cobbles and boulders. Locally contains lenses and stringers of moderately well sorted clay, silt, sand, or gravel. Thickness generally less than 30 ft, but as much as 100 ft.

Qgo

Glacial outwash deposit (Pleistocene)—Light-brown, yellowish-brown, brown, and light-gray, fine-grained sand, silt, and clay in glacial meltwater and stream-diversion channels. Thickness not determined. May be more than 50 ft thick in places (Prichard and Landis, 1975).

Qgl

Glacial lake deposit ? (Pleistocene)—Assumed deposit obscured by younger fine-grained alluvium and colluvium. Thickness not determined.

Qgk

Glacial kame deposit—(from Prichard and Landis, 1975) Chaotically cross- bedded cobbles, pebbles, and sand in rounded hills. Thickness not determined.

Qge

Glacial esker deposit—(from Prichard and Landis, 1975) Cross-bedded gravel, sand, silt, and clay in sinuous ridges. Thickness not determined.

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