Willwood Formation
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene. It consists of fine grained clastic rocks interbedded with medium grained clastic rocks and sporadic conglomerates. The formation underlies portions of the Bighorn Basin of Big Horn, Hot Springs, Park and Washakie counties of Wyoming.
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.
Trace fossils have been found in the Willwood Formation. Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.
