The coal and uranium resource potential of the western Yukon flats was investigated by the Bureau of Mines during the 1978-79 field seasons. Previously, the mineral endowment of the area was largely unknown and there existed only partial 1:250,000-scale geologic reconnaissance mapping. The Yukon flats is an extensively vegetated sedimentary basin of interior Alaska in which terrigenous sediments have been accumulating since eocene (?) time. Preliminary evidence presented in this report suggests that sedimentation apparently has been taking place under climatic conditions typical of the mid- Tertiary at higher latitudes elsewhere. Conditions then were warm to paratropical and may have varied to rather hot and arid. Evidence includes relatively thick coal formations, the extensive occurrence of nonmarine evaporite minerals, undated but typical of continental arid saline lakes, stratiform tungsten enrichment, and fossil data that was previously reported.