Coors Crag

Rock, from the geologic map

Valley-floor alluvium. Quaternary, younger than 126,000 years.

Mostly poorly sorted coarse sand and pebbly to bouldery cobble gravel in stream channels, flood plains, and low terraces in mountain valleys. Flood-plain and terrace deposits of Holocene age are commonly about 1.3 m or less above present streams (Madole, 1996). Unit locally includes a minor amount of young stream-terrace alluvium (Qg1), colluvium (Qc) and other mass-movement deposits, fan deposits (Qf), and glacial deposits (Qtp and Qti) along valley margins and organic-rich sediments in bogs, marshes, and meadows. Locally may include minor lake sediments. Top of unit probably consists mostly of poorly sorted sand and gravel in nonglaciated valleys. Unit is commonly less than 5 m above the Fraser River and tributary streams near Fraser and Tabernash, Colo., and commonly less than 5 m above present streams elsewhere within map area. Low-lying deposits are prone to periodic flooding. Estimated thickness 5–10 m

This is the map unit under this crag's map point, read from the 1:100,000 sheet (Kellogg and others, 2008, USGS Geologic Investigations Series 3000). The point can be a few hundred metres from the rock, a cliff often stands on the line between two units, and at that scale a line on the map is about 100 m wide on the ground, so the wall itself may be the neighbouring unit. Every crag on this unit: Valley-floor alluvium. Geology data: Macrostrat (CC BY 4.0), serving USGS and Colorado Geological Survey maps.