The purpose of the CGS Open-File Report OF-16-06, Geologic Map of the Roubideau Quadrangle, Delta and Montrose Counties, Colorado is to describe the geology, mineral and ground-water resource potential, and geologic hazards of this 7.5-minute quadrangle located on Colorado’s Western Slope. The geologic map plates were created using field maps, structural measurements, photographs, and field notes generated by the investigators. Includes 2 plates (map, cross-section, and 3-D oblique view) and GIS data in a single zip file. Digital ZIP download. OF-16-06D
A few small reservoirs and tributary creeks feed into the Gunnison River, which traverses the northern portion of the Quadrangle. The Gunnison River is associated with six terrace levels in the northern part of the quadrangle. Alluvium six of the Gunnison River is not in the quadrangle, but its prior existence is inferred by the presence of an alluvium of the Uncompahgre River at this level indicating a confluence of the two rivers at the time of deposition of alluvium six. Due to down cutting by the river, these terraces extend as much as 435 feet above the current river elevation.
Mass wasting deposits are found in two general locations: along the steep slopes below the edges of the gravel-capped mesas and terrace remnants, and within the plateau canyons on the canyon walls where weak mudstones of the Morrison Formation have failed. Exposed bedrock units range in age from Upper Cretaceous (Mancos Shale) to Jurassic (Morrison Formation). These are composed of shales, mudstones and sandstones.