OF-22-11 Geologic Map of the Mount Blue Sky (formerly Mount Evans) Quadrangle, Clear Creek and Park Counties, Colorado

The purpose of this map is to describe the geology, mineral and ground-water resource potential, and geologic hazards of this 7.5-minute quadrangle located west-south-west of Denver, and south of Georgetown, Colorado. The quadrangle includes the iconic Mount Blue Sky (formerly Mt. Evans), a 14,271-foot (4,350 m) peak visible 100 miles east from the Great Plains. The map adds to our geologic coverage of the area which includes the Georgetown and Idaho Springs quads. Field work for the project was conducted between 2017 and 2019. The GIS data included in this package is GeMS Level 3 compliance as of November 2022. Includes 2 plates and GIS data in a single zip file. Digital ZIP download. OF-22-11D

This mapping project was funded jointly by the CGS, the United States Geological Survey, and the Colorado School of Mines through the National Cooperative Geologic Mapping Program under EDMAP agreement numbers G17AC00143 and G18AC00130. The CGS matching funds come from the severance paid on the production of natural gas, oil, coal, and metals. EDMAP is the component of the NCGMP that funds universities to train the next generation of geologic mappers. EDMAP is a one-year, mentor-guided program designed to teach students geologic mapping techniques through rigorous field mapping.

From the Geologic Setting:

The Mount Blue Sky (formerly Mount Evans) 7.5′ quadrangle lies in Park and Clear Creek counties, Colorado, about 60 km west of Denver. The highest elevation in the quadrangle is 14,265 ft (4,348 m) at the top of Mount Blue Sky. The lowest is at about 9,200 ft (2,804 m) on Guanella Pass Road at the southern edge of the quadrangle. Bedrock directly underlies most of the map area, with surficial deposits primarily in the valleys. The geology of the quadrangle was previously mapped at 1:100,000 scale as part of a regional compilation by Kellogg and others.

The oldest rocks in the Mount Blue Sky 7.5-minute quadrangle are Paleoproterozoic metasedimentary rocks, and mafic to felsic metaigneous rocks (all units starting w ith ‘X’ on Plate 1). These rocks were metamorphosed under upper amphibolite facies conditions and intruded by Mesoproterozoic felsic igneous rocks of the ~1442 Ma Mount Evans (YgR, Yt, Ygdm, Ymgm) and ~1424 Ma Silver Plume (Yg) batholiths and, in the southern part of the quadrangle, by rocks that may also be part of the Mount Evans batholith, but may alternatively interpreted as part of the ~1115 Ma to ~1066 Ma Pikes Peak batholith.