Named for metasedimentary rocks--quartzite, phyllite, metaconglomerate, schist, slate--present at the head of Libby Creek, east side Medicine Bow Mountains, T16N, R79W, Albany Co, WY in Northern Rocky Mountain region. No type locality designated. Includes all metasedimentary rocks younger than the Deep Lake Formation (ascending order)--the Headquarters Schist, Heart Formation (formerly Heart Metagraywacke), Medicine Peak Quartzite, Lookout Schist, Sugarloaf Quartzite, Nash Fork Formation, Towner Greenstone, and French Slate. Geologic map; stratigraphic charts. Contact between quartzite of Deep Lake and interbedded phyllite and metaconglomerate of Headquarters is conformable. In T15N, R81W to southwest beyond the outcrop limit of the Deep Lake and the Headquarters, Heart rests on Precambrian basement gneiss. Is about 22,000 ft thick in central Medicine Bows. Sequence of units determined largely from crossbreeding in quartzite. Rank of metamorphism and intensity of deformation increases to southwest and to a lesser extent to the northeast. Of Precambrian age.

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

Is represented in the Sierra Madre Range by an E-W trending, fault bounded anticlinorium of isoclinally folded sedimentary rocks. Original thickness exceeds 4,300 m. Eighty-five percent of the group is quartzite. Divided into five newly named formations (ascending order): Cow Creek Conglomerate, Bridger Pass Quartzite, Copper Creek Conglomerate, Quartzite Peak Quartzite, and Slaughterhouse Marble. Columnar section. Separated from underlying Green Mountain Formation by a structural unconformity. Top of group is irregular, bounded by low angle faults. Most complete sections are in cirques in Bridger Peak area, T14N, R86W and Cow Creek Reservoir, T14N, R85W. Difficult to establish correlation with units in Medicine Bow Range. Group does have well preserved graded bedding, cross-bedding, and cut-and-fill features. Geologic map; all five formations mapped as one unit. Assigned to the Proterozoic.

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

Lower contact revised in the Medicine Bow Mountains, Albany and Carbon Cos, WY in the Northern Rocky Mountain region, in that the Headquarters Formation of Libby Creek Group unconformably overlies the newly named Rock Knoll Formation of the Deep Lake Group (raised in rank from Deep Lake Metaquartzite). The Headquarters is divided into a lower member, 1,120 ft thick, probably deposited in a glacio-marine environment and an upper member, 980 ft thick, deposited either in a large lake or in a marine environment. Overlying parts of Libby Creek not described. Headquarters mapped in central Medicine Bow Mountains. Libby Creek is of Early Proterozoic age. Geologic map; stratigraphic charts.

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

Overlies newly named Rock Knoll Formation of Deep Lake Group in Northern Rocky Mountain region. Assigned to Proterozoic.

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

Name no longer used in the Sierra Madre. In the Medicine Bow Mountains, group revised to include the Rock Knoll Formation at base. Rock Knoll formerly included in underlying Deep Lake Group is reassigned to the Libby Creek because its basal contact is a thrust fault with the Vagner Formation (now the upper formation of the Deep Lake) and the upper contact with Headquarters Formation of Libby Creek Group is depositional. Formations above the Rock Knoll that are assigned to Libby Creek are (ascending): Headquarters and Heart Formations, Medicine Peak Quartzite, Lookout Schist, and Sugarloaf Quartzite of the lower part of the Libby Creek, and the Nash Fork Formation, Towner Greenstone, and French Slate of the upper part of the Libby Creek. All rocks assigned are primarily silici-clastic metasedimentary and largely marine, except for Towner which consists of volcanic rocks. Two parts separated by the Lewis Lake fault. Lower part cut by Gaps Intrusion of about 1,950 Ma. Assigned to the Early Proterozoic. Geologic map; stratigraphic charts.

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