The Raben Ranch local fauna is the largest early Oligocene (Chadronian) vertebrate fauna ever collected from a single locality in the High Plains and has yielded over 12,000 specimens. The fossils occur in the middle part of the Chadron Formation of northern Sioux County, Nebraska. New taxa described include a bat, Chadronycteris rabenae n. gen. et sp.; a mammal of unknown affinities. Idiogenomys ozziei n. gen. et sp.; an insectivore, Micropternodus montrosensis n. sp.; and two rodents, Cylindrodon galbreathi n. sp. and Cupressimus storeri n. sp.--Journal abstract.