WSP02105

• File Number: 8200.765
• Description: White River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 5/1/1986
• Author: Morrison-Knudsen
• Title: White River Geotechnical Study - Final Report - Volume I
• Water Supply Pro - Doc Type: Report/Study

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the White River. Generally, these deposits are unconsolidated, poorly sorted,
and contain rounded, sand-to cobble-size ~lasts of varying composition.
Terraces unconformably overlie bedrock and have thicknesses less than 50 feet.

Terraces are more extensi ve at lower e1 evati ons, where the youngest terraces
exhibit less erosion or are covered by still younger colluvium and alluvial
fans. At higher elevations, slope wash and development of small drainages
have left only small remnants of previously extensive terraces.

Unlike other Quaternary units whose source material is in close proximity to
the deposit, terrace gravel s are derived from erosional detritus of many
exposed bedrock formations in the White River drainage basin. The deposits
are formed as post-glacial alluvial outwash from glacial deposits upstream
that provide the source for stream-transported sediment.

Alluvial Fan Deposits (Qf)
Alluvial fans occur at the mouths of small streams draining into the White
River. These are evenly-sloped, fan-shaped deposits. The areal extent and
thickness of fans is proportional to the area of the drainage basin serving as
the sediment source: In some areas, older alluvial fans have completely
covered porti ons of stream terraces and small er secondary fans have developed
on the next lower terrace. The fans are most pronounced in the downstream
study area below Powell Park.

Alluvial fan material is unconsolidated, crudely stratified or massive, and
poorly sorted at the heads of fans changing to moderately sorted at the base.
Grain sizes range from silt to pebble-size clasts, probably because granular
disintegration and transport of sedimentary rocks tends to produce finer
grained deposits than would denser, more resistant rock that form the terraces.

Colluvial Deposts (Qc)
As rock outcrops weather and disintegrate, pluvial and creep processes
transport material to the bases of slopes. The transported material, or
coll uvi um, is a poorly-sorted mi xture contai ni ng angular fragments of all

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