Occurrence of lower Oligocene mammal-bearing beds near Death Valley, California

It is a curious fact that while the White River deposits with their wealth of vertebrate fossils are widely distributed in the western Great Plains and occur also in certain of the intermontane basins of the Cordilleran province, no horizon, recognized on the basis of land mammals as equivalent in time to the lower Oligocene or Titanotherium Zone, has been found beyond these areas on the North American continent.(1) All the more unusual does this fact seem when it is realized that since the definition of the White River Group by Hayden in 1862 and the early researches on the White River fossil vertebrates by Leidy, Cope and Marsh, field investigations in the Tertiary have progressed broadly and intensively over the Far West.