Soil Formations: Geologic Classes and Characteristics - Geotechnical Engineering Investigation - page 498

TABLE 7.2
( Continued )

Origin of Symbol Physiographic Physiographic Features Characteristic Soil

Principal for Area Province Deposits

Soil Deposits in Figure 7.1

Residual R5 Northern and Old plateau, terrace Soils weathered in place

western sections lands, and Rocky from shale, sandstone,

of Great Plains Mountain piedmont and limestone including

province areas of clay shales in

Montana, South Dakota,
Colorado

Residual R6 Wyoming basin Elevated plains Soils weathered in place

from shale, sandstone,
and limestone

Residual R7 Colorado plateaus Dissected plateau of Soils weathered In place

strong relief from sandstone

primarily, shale and
limestone secondarily.

Residual R8 Columbia High plateaus and Soils weathered from

plateaus and piedmont. extrusive rocks in

Pacific border Columbia plateaus and

province from shale and sandstone

on Pacific border. Includes
Includes area of volcanic
ash and pumice in
central Oregon

Loessial L1 Portion of coastal Steep bluffs on west 30 to 100 ft of loessial silt

plain limit with incised and sand overlying coastal

drainage plain alluvium. Loess

cover thins eastward

Loessial L2 Southwest section Broad intervalley Loessial silty clay, silt,

of central remnants of smooth silty fine sand with

lowland: portions plains clayey binder in western

of Great Plains areas, calcareous binder

in eastern areas

Loessial L3 Snake River plain Young lava plateau Relatively thin cover of

of Columbia loessial silty fine sand

plateaus overlying fresh lava flows

Loessial L4 Walla Walla Rolling plateau with Loessial silt as thick as 75

plateau of young incised valleys ft overlying basalt. Incised

Columbia valleys floored with

plateaus coarse-grained alluvium

Glacial G1 New England Low peneplain maturely Generally glacial till

Province eroded and glaciated overlying metamorphic

and intrusive rocks,
frequent and irregular
outcrops. Coarse,
stratified drift in upper
drainage systems. Varved
silt and clay deposits at
Portland, Boston, New
York, Connecticut River
Valley, Hackensack area

Glacial G2 Northern section Mature glaciated Generally glacial till

of Appalachian plateau in northeast, overlying sedimentary

plateau, Northern young till plains in rocks. Coarse stratified

section of Central western areas drift in drainage system.

lowland Numerous swamps and

marshes in north central