OF-20-02 Geologic Map of the Agate Mountain Quadrangle, Park 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 located in the South Park region near the south- and easternmost extent of the Front Range. This quadrangle was mapped by CGS geologists Karen Houck, Jay Temple, Kassandra Lindsey, Lauren Broes, and Daniel Miggins. Digital ZIP download. OF-20-02D

From the abstract:

The Agate Mountain quadrangle contains Proterozoic igneous and metamorphic rocks, Paleozoic sedimentary rocks, and Cenozoic volcanic and volcaniclastic rocks. Proterozoic rocks include granite, granitic gneiss, gabbro porphyry, pegmatite, mylonite, and microbreccia. Paleozoic sedimentary rocks include the Manitou Formation, Harding Sandstone, Fremont Formation, Dyer Dolomite, Leadville Limestone, Belden Formation, Minturn Formation, and Maroon Formation. Cenozoic volcanic and volcaniclastic rocks include Wall Mountain Tuff, Thirtynine Mile Andesite, volcanic breccias, trachybasalt, Tallahassee Creek Conglomerate, Antero Formation, Gribbles Park Tuff, and Wagontongue Formation. The quadrangle also contains a variety of alluvial and mass-wasting deposits, as well as a few human-made deposits. It spans portions of three major, fault-bounded, structural blocks: Kaufman Ridge, the Wagon Tongue graben, and the Hartsel uplift. Each has a different stratigraphy, and a different geologic history. Kaufman Ridge contains a thick section of Paleozoic rocks, but relatively few Cenozoic rocks and surficial deposits. The Wagon Tongue graben contains a relatively thin section of upper Paleozoic rocks, as well as a thick section of Cenozoic volcanic and volcaniclastic rocks. Gravel deposits derived from both uplifts are numerous in the graben, as are debris flow deposits. The Hartsel uplift contains scattered erosional remnants of upper Paleozoic rocks, as well as a relatively thin section of Cenozoic volcanic and volcaniclastic rocks. Gravel deposits are common along Agate and Little Agate creeks. It is inferred that the three structural blocks were most active during the ancestral Rockies orogeny, the Laramide orogeny, and the opening of the Rio Grande rift. Geologic hazards on the quadrangle include flooding, sinkholes, collapsible soils, landslides, debris flows, and falling rocks.