OF-21-03 Geologic Map of the Dry Creek Quadrangle, Delta County, Colorado

The purpose of this publication is to describe the geology, geologic resources, and geologic hazards of this 7.5-minute quadrangle. It is a continuation of field mapping work in the Grand Valley and Grand Mesa areas of the Western Slope of Colorado where the CGS has cumulatively mapped 22 other quadrangles in the past. These include Cedaredge, Lazear, Hotchkiss, and Orchard City in the immediate vicinity. CGS Senior Geologist Jon White (Emeritus) completed the field work on this project during the mapping seasons of 2021-22. Digital ZIP download. OF-21-03D

From the Abstract:

The Dry Creek quadrangle, situated on the southern flank of Grand Mesa in Delta County Colorado, features high topographic relief with a 1,246.7-m (4,090 ft) variance between its highest and lowest points. The slopes in the upper third of the map area are part of the southern flank of Grand Mesa and are characterized by higher elevations and hummocky, south-facing slopes where landslide deposits overlay Paleogene to Eocene Green River and Wasatch formations. The upper hummocky terrain transitions southward to cliffy mid-elevation sandstone outcrops of the Upper Cretaceous Williams Fork and Iles formations. A regional productive coal interval, the Cameo/Wheeler coal zone, occurs in this interval above the Rollins Sandstone Member of the Iles Formation. In the lower valleys and southern part of the map area, bouldery gravel mantle low-gradient mesa and river terrace surfaces that cover the Upper Cretaceous Mancos Shale. Landslides also occur along steeper slopes of the mesa flanks and terrace risers. The highest elevation of the Dry Creek quadrangle is 3.097.0 m (10,160.8 ft) above mean sea level (AMSL) at the northeast map corner within the Grand Mesa National Forest. The lowest is 1,850.3 m (6,070.5 ft) AMSL at its southwest boundary. The annual precipitation in the map area ranges from about 100 cm (40 in) along the northern map area where alpine forests are predominant, through a mid-elevation semi-arid Gambel oak, pinyon- juniper, woodland climate of the high alluvial mesas, to a low of about 33 cm (13 in) at lower- elevation semi-arid shrublands in the southwest corner of the map area. Seasonal snowpack occurs in the high country of the map area.