It consists of fine grained clastic rocks (
mudstone and
shale) interbedded with medium grained clastic rocks (
sandstone) and sporadic
conglomerates. The formation underlies portions of the
Bighorn Basin of
Big Horn,
Hot Springs,
Park and
Washakie counties of
Wyoming.
Dating Radiometric dating of volcanic tuffs, combined with comparisons with other formations using magnetostratigraphy, using numerous samples from various levels of the formation suggest an age range of 55 – 52 million years ago, placing the Paleocene-Eocene boundary near the base of the formation. == Fossil content ==