Named as the lowest member (of three) of the Manitou limestone for exposures in Helena Canyon, T. 16 S., R. 70 W., Fremont Co, CO in the Denver basin. Type section measured in sec. 22, T. 16 S., R. 70 W., along the Shelf Road in Cripple Creek where Helena Canyon is 12.5 ft thick, and where it unconformably overlies Precambrian schist and gneiss and underlies the cherty member of the Manitou. Consists of pink, massive to blocky dolomite. Contains no chert. Basal contact is a regolith or thin zone of weathering. Includes a basal conglomerate of subangular to rounded cobble-size quartz fragments in a limestone matrix at some places. Considered to be Early Ordovician in age. Columnar section, geologic map, cross section.

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

Name Horseshoe Mountain Group applied to rocks of the Sauk sequence in central CO of Late Cambrian and Early Ordovician age. In its northwest province near Glenwood Springs, Garfield Co in the Piceance basin, the group is divided into the Sawatch Sandstone, Dotsero Formation (and its Glenwood Canyon and Clinetop Members), and Manitou Limestone (and its Deadhorse and Tie Gulch Members). In its southeast province--near Salida, Gunnison Co in the Piceance basin, Colorado Springs, El Paso CO in the Denver basin, and Fairplay, Park Co in the South Park basin--the group is divided into the Sawatch Sandstone, Peerless Formation, and Manitou Limestone (and its Helena Canyon, Ptarmigan (provisional), and Fairplay (provisional) Members). The group is named for exposures on Horseshoe Mountain (the type section) near Fairplay in Park Co. Rocks of the group include conglomerate, sandstone, shale, limestone, and dolomite. Correlation chart. Thickness of group at type (southeast facies--sec. 12, T. 10 S., R. 79 W.) is 352 ft: Manitou, 167 ft; Peerless, 35 ft; and Sawatch, 150 ft. Thickness of group in northwest facies (sec. 15, T. 5 S., R. 87 W.) is 772 ft: Manitou, 156 ft; Dotsero, 96 ft; and Sawatch, 520 ft.

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

Upper contact revised in that Helena Canyon Member, basal member of Manitou Formation, unconformably underlies the newly named Ptarmigan Chert Member of the Manitou in its southeastern facies. Manitou, formerly designated Manitou Limestone, is assigned as the upper formation of the Horseshoe Mountain Group. Helena Canyon overlies Peerless Formation, middle formation of the Horseshoe Mountain Group. Described in two measured sections as a gray, tan, pink, very thin bedded, blocky, finely laminated to massive dolomite. Some of the dolomite beds are coarse grained. Is 20.7 ft thick at type section of Manitou in SW/4 sec. 32, T. 13 S., R. 67 W., El Paso Co, CO in the Denver basin. Is 23.6 ft thick at type section of the Ptarmigan Chert and Leavick Tarn Dolomite (new) Members in secs. 7 and 18, T. 10 S., R. 78 W., Park Co, CO in the South Park basin. Of Early Ordovician age. Correlated with lower part of Deadhorse Conglomerate Member of Manitou in its northwestern facies.

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