Named for Heart Lake, T16N, R79W, Albany Co, WY in the Northern Rocky Mountain region. No type locality designated. No full section described. Sections from several outcrops described as a gray-white, olive-gray to dark-gray metaquartzite. Is 1,515 ft thick. May be massive to thin bedded. Has thin schistose layers and pyrite cubes. Some beds are cross-bedded, and some have current marks. Is not very resistant to erosion. Is younger than Headquarters schist (new); contact is conformable. Is older than Medicine Peak metaquartzite (new); contact is conformable. Is of pre-Cambrian age, probably early Algonkian or Proterozoic.

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

Revised in that Heart Formation is assigned (1 of 6 formations) to the lower part of the Libby Creek Group of the Snowy Pass Supergroup (first used) in the Medicine Bow Mountains of south-central WY in the Northern Rocky Mountain region. Lies between the Headquarters Formation (below) and the Medicine Peak Quartzite (above). Is a 670 m thick predominantly quartzite unit. A 90 m thick phyllite occurs locally about 400 m above the base. The quartzite is sericitic, very fine to medium grained and becomes quartzose near top. Has planar and trough crossbeds, and climbing, interference, and symmetric ripples, ball and pillow structures, and graded bedding. Interpreted as a pro-delta and delta-front deposit. Sediment transport primarily from southwest. Geologic map; stratigraphic chart. Proterozoic age.

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

Assigned in the Medicine Bow Mountains, Carbon and Albany Cos, WY, Northern Rocky Mountain region, as one of six formations of the lower part of the Libby Creek Group of the newly defined Snowy Pass Supergroup. Conformably overlies Headquarters Formation of lower part of Libby Creek. Conformably underlies Medicine Peak Quartzite of lower part of Libby Creek. Is 670 m thick. Correlated with part of Bottle Creek Formation (new) of Snowy Pass Group of the Sierra Madre. Correlation chart. Geologic map. Of Early Proterozoic age.

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