Curve Block

Rock, from the geologic map

Landslide deposits. Quaternary, younger than 781,000 years.

Deposits of unsorted and unstratified debris, on slopes or at base of slopes, that are commonly characterized by hummocky topography. Many of the landslides and landslide deposits form on unstable slopes that are underlain by shale, siltstone, and claystone on east flank of hogback belt and on slopes of North Table Mountain and South Table Mountain near Golden. Younger deposits are commonly bounded upslope by crescent-shaped headwall scarps and downslope by lobate toes. Unit locally includes material displaced chiefly by rotational rock slides, rotational earth slides, debris slides, earth flows, and earth slide–earth flows as defined by Varnes and Cruden (1996). Some deposits probably are formed by translational slides and rock or earth creep. Sizes and lithologies of clasts and grain-size distributions of matrices of these deposits reflect those of the displaced bedrock units and surficial deposits. Landslide deposits are prone to continued movement or reactivation due to natural, as well as human-induced, processes. Deposits in mountainous terrain derived from Precambrian quartz-feldspar gneiss (Xf) and biotite gneiss (Xb) locally contain blocks of rock as long as several meters. Landslide deposits derived from Pierre Shale (Kp), Laramie Formation (Kl), and Denver Formation (bKd) are rich in clay. Some of this clay is expansive and locally may have high potential for shrinking and swelling (Shroba, 1982). Deposits on gentle slopes along and east of hogback belt locally include minor sheetwash and creep-deformed deposits. Deposits in mountains locally include minor rock-fall deposits. Estimated thickness 5–50 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: Landslide deposits. Geology data: Macrostrat (CC BY 4.0), serving USGS and Colorado Geological Survey maps.