Colluvium

What the map says

Deposits of rock debris ranging in size from silt to boulders, formed by a variety of mass-wasting processes. Includes older talus, slopewash deposits, solifluction deposits, block fields, and nivation scree. Although most slopes are mantled by a thin layer of colluvium and contain only scattered exposures of bedrock, colluvium has been mapped only in those areas where it is several meters thick or where it covers large areas and obscures the continuity of bedrock units. GRI Source Map ID 141 (I- 1973). Lithology: unconsolidated.

1:100,000 sheet: National Park Service Geologic Resources Evaluation program, 2006, National Park Service (2 crags). A contact line at that scale is about 100 m wide on the ground.

Generally unconsolidated material deposited on slopes by gravity and sheetwash. Thickness generally more than 1.5 m. Includes talus.

1:100,000 sheet: Trimble and others, 2003, U.S. Geological Survey Geologic Investigations Series I-856-H (2 crags). A contact line at that scale is about 100 m wide on the ground.

Bouldery to pebbly sandy silt and clay deposited by gravity and sheet wash on slodes. Color and texture of colluvium reflects parent material. May contain and interfinger with alluvium of various ages. Thickness as much as 25 feet (7.5 m) but generally n

1:100,000 sheet: Colton, Roger B., 1976, U.S. Geological Survey Geologic Investigations Series I-855-G (2 crags). A contact line at that scale is about 100 m wide on the ground.

Non-sorted deposits that consist of clay, silt, sand, and clasts that range in size from granules to large boulders, formed by a variety of mass-movement processes. Unit Qc chiefly includes small deposits in and near the foothills hogback belt and on slopes in montane areas, as well as extensive areas of block-slope deposits near and above present day treeline at about 3,475 m where freeze-thaw action has promoted mass-movement and downslope transport. The composition of the deposits reflect that of the bedrock or sediment from which the colluvium was derived. Unit Qc includes material transported by frost creep, solifluction, nivation and other periglacial processes, sheetwash, landslide, debris flow, hyperconcentrated flow, and rock fall. Unit Qc locally includes small bodies of undifferentiated valley-floor alluvium (Qa), mountain-valley alluvium (Qva), pediment deposits (Qp), sheetwash alluvium (Qsw), landslide deposits (Qls), and talus deposits (Qta). Estimated thickness is 3–15 m Lithology: colluvium.

1:100,000 sheet: Workman and others, 2018, U.S. Geological Survey Scientific Investigations Map 3399 (1 crag). A contact line at that scale is about 100 m wide on the ground.

Unconsolidated to weakly consolidated, mostly non-stratified and non-sorted, dark-brown to light-gray-brown deposits that mantle surfaces that commonly underlie slopes less than about 40°. Clasts and finer- grained sediment are transported and deposited mainly by downslope movement. Unit commonly contains angular and subangular granule- to boulder-sized clast with lithologic compositions that reflect that of bedrock and clasts in surficial deposits farther upslope. Unit includes material transported by creep, sliding, debris flow, hyperconcentrated flow, rockfall and rockslide processes. Unit locally includes minor unmapped deposits of stream-channel and sheetwash alluvium. In the southern part of the map area, unit Qc is locally overlain by thin, unmapped, loess deposits as much as 50 cm thick that are composed chiefly of very fine sand and silt. Unit locally includes extensive mass-movement deposits formed by periglacial processes mainly during glacial episodes (chiefly solifluction and ice wedging) in non-glaciated, alpine areas above an elevation of about 3,500 m. The upper part of these latter deposits consists of material derived chiefly from mechanical weathering of blocks and smaller rock fragments and, in part, from the deposition of loess. Surface of periglacial deposits commonly exhibit patterned ground features produced by particle sorting chiefly by near-surface frost sorting and ice wedging. Kellogg and others (2013) mapped extensive periglacial deposits in high country surrounding Buffalo Peaks in the Harvard Lakes quadrangle. Many deposits of unit Qc mapped above treeline throughout the map area probably are composed of or locally include periglacial deposits. At lower elevations, deposits of unit Qc are locally common in open meadows, sagebrush-covered areas, and aspen groves. Estimated thickness is less than 10 m Lithology: colluvium.

1:100,000 sheet: Kellogg and others, 2017, U.S. Geological Survey Scientific Investigations Map 3382 (1 crag). A contact line at that scale is about 100 m wide on the ground.

Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.