Named for Ralston Buttes, Ralston Buttes quad, Jefferson Co, CO in the Southern Rocky Mountain region. Type area designated as exposures in sec 25, T2S, R70W. Geologic map. Cross sections. Occurs only in northern part of area. Dips 50 to 85 degrees southwest under Belcher Hill Formation (new). Is the oldest metasedimentary unit in report area. Consists essentially of amphibolitic, thin-bedded gneiss containing minor intercalations of epidote-garnet tactites and fine-grained quartzites. The tactites commonly weather into bone-like structure. Thin quartz and granite lenses occur throughout. Concordant and discordant coarse-textured pegmatites as much as 40 ft thick occur at many localities. Probably exceeds 7,000 ft along mountain front but diminishes rapidly to northwest. Called amphibolite unit in earlier reports. Precambrian age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is one of several units defined in a narrow belt along east-central Front Range, near Golden, Jefferson Co, CO in the Southern Rocky Mountain region. Of doubtful use elsewhere. Assumed direction of stratigraphic sequence is debatable. Belongs with pre-1,700 m.y. metamorphic complex, or of Precambrian X age.

Source: GNU records (USGS DDS-6; Denver GNULEX).