Geology topics

Research about Garfield, Colorado

Source-linked reports with geographic coverage including Garfield, Colorado.

2 recordsLinked to original sources

USGS2001

Geologic map of the Silt quadrangle, Garfield County, Colorado

New 1:24,000-scale geologic mapping in the Silt 7.5' quadrangle, in support of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping Project, provides new interpretations of the stratigraphy, structure, and geologic hazards in the area of the southwest flank of the White River uplift, the Grand Hogback, and the eastern Piceance Basin. The Wasatch Formation was subdivided into three formal members, the Shire, Molina, and Atwell Gulch Members. Also a sandstone unit within the Shire Member was broken out. The Mesaverde Group consists of the upper Williams Fork Formation and the lower Iles Formation. Members for the Iles Formation consist of the Rollins Sandstone, the Cozzette Sandstone, and the Corcoran Sandstone Members. The Cozzette and Corcoran Sandstone Members were mapped as a combined unit. Only the upper part of the Upper Member of the Mancos Shale is exposed in the quadrangle. From the southwestern corner of the map area toward the northwest, the unfaulted early Eocene to Paleocene Wasatch Formation and underlying Mesaverde Group gradually increase in dip to form the Grand Hogback monocline that reaches 45-75 degree dips to the southwest (section A-A'). The shallow west-northwest-trending Rifle syncline separates the northern part of the quadrangle from the southern part along the Colorado River. Geologic hazards in the map area include erosion, expansive soils, and flooding. Erosion includes mass wasting, gullying, and piping. Mass wasting involves any rock or surficial material that moves downslope under the influence of gravity, such as landslides, debris flows, or rock falls, and is generally more prevalent on steeper slopes. Locally, where the Grand Hogback is dipping greater than 60 degrees and the Wasatch Formation has been eroded, leaving sandstone slabs of the Mesa Verde Group unsupported over vertical distances as great as 500 m, the upper part of the unit has collapsed in landslides, probably by a process of beam-buckle failure. In the source area of these landslides strata are overturned and dip shallowly to the northeast. Landslide deposits now armor Pleistocene pediment surfaces and extend at least 1 km into Cactus Valley. Gullying and piping generally occur on more gentle slopes. Expansive soils and expansive bedrock are those unconsolidated materials or rocks that swell when wet and shrink when dry. Most floods are restricted to low-lying areas. Several gas-producing wells extract methane from coals from the upper part of the Iles Formation.

Colorado↗

USGS1997

Revised preliminary geologic map of the Rifle Quadrangle, Garfield County, Colorado

The Rifle quadrangle extends from the Grand Hogback monocline into the southeastern part of the Piceance basin. In the northeastern part of the map area, the Wasatch Formation is nearly vertical, and over a distance of about 1 km, the dip decreases sharply from about 70-85o to about 15-30o toward the southwest. No evidence of a fault in this zone of sharp change in dip is observed but exposures in the Shire Member of the Wasatch Formation are poor, and few marker horizons that might demonstrate offset are distinct. In the central part of the map area, the Shire Member is essentially flat lying. In the south and southwest part of the map area, the dominant dip is slightly to the north, forming an open syncline that plunges gently to the northwest. Evidence for this fold also exists in the subsurface from drill-hole data. According to Tweto (1975), folding of the early Eocene to Paleocene Wasatch Formation along the Grand Hogback reqired an early Eocene age for the last phase of Laramide compression. We find the attitude of the Wasatch Formation to be nearly horizontal, essentially parallel to the overlying Anvil Points Member of the Eocene Green River Formation; therefore, we have no information that either confirms or disputes that early Eocene was the time of the last Laramide event. Near Rifle Gap in the northeast part of the map area, the Mesaverde Group locally dips about 10o less steeply than the overlying Wasatch Formation, indicating that not only had the formation of the Hogback monocline not begun by the time the Wasatch was deposited at this locality, but the underlying Mesaverde Group was locally tilted slightly toward the present White River uplift. Also the basal part of the Atwell Gulch Member of the Wasatch Formation consists of fine-grained mudstones and siltstones containing sparse sandstone and rare conglomerates, indicating that the source of sediment was not from erosion of the adjacent Upper Cretaceous Mesaverde Group. The most likely source of andesitic conglomerate clasts abundant in the upper part of the Atwell Gulch Member was Late Cretaceous-Early Tertiary andesitic igneous rocks, remnants of which are present southeast of the Piceance Basin (Tweto, 1979). Thinning of the Atwell Gulch and Molina Members to the northwest also suggests a southeastern source of sediments, ruling out a northeastern source related to earlier deformation of the Upper Cretaceous Mesa Verde Group.

Colorado↗