For over a century the Bridger Formation of southwestern Wyoming has yielded fossils of many important middle Eocene vertebrate taxa. This formation is of particular interest to the study of ancient primates because their remains are plentiful. In fact, the first fossil primates described from the Western Hemisphere, Omomys carteri and Notharctus tenebrosus were found here (Leidy, 1869, Leidy, 1870). Arguably, the premier fossil collecting locale within the Green River Basin is an area known as Grizzly Buttes (Figure 1). Although the place name has disappeared from official maps and the local lexicon (West, 1990), it is well established in the paleontological literature. The area has a rich history. Both O. C. Marsh and E. D. Cope collected from these outcrops in the 1870′s extending their professional rivalry to the description of Bridgerian mammals (Wheeler, 1961). The area is figured by H. F. Osborn (1910) as the “famous” locality of Grizzly Buttes.