INTRODUCTION

Fossil mammals preserved in distal volcaniclastic sediments of the Ohanapecosh Formation record late Eocene and Oligocene terrestrial environments in the Tieton River area, located 30 miles southeast of Mount Rainier in south central Washington (Figure 1). Fieldwork since the 1930s resulted in the collection of 34 specimens of terrestrial mammals along Wildcat Creek and one specimen along Milk Creek. These fossils are the oldest non-marine mammals recovered from Washington and represent a new data point to examine the biogeography of mammals in North America. This study is the first detailed description of the specimens and seeks to understand them by developing a stratigraphic and paleoenvironmental framework.