The Screw Bean Local Fauna is the earliest Hemphillian fauna of the southwestern United States. The fossil remains occur in all parts of the informal Banta Shut-in formation, nowhere very fossiliferous. The formation is informally subdivided on the basis of stepwise fining and slowing deposition into Lower (least fossiliferous), Middle, and Red clay members, succeeded by the valley-filling, Bench member (most fossiliferous).

Identified Carnivora include: cf. Pseudaelurus sp. and cf. Nimravides catocopis, medium and large extinct cats; Epicyon haydeni, large borophagine dog; Vulpes sp., small fox; cf. Eucyon sp., extinct primitive canine; Buisnictis chisoensis, n. sp., extinct skunk; and Martes sp., marten. B. chisoensis may be allied with Spilogale on the basis of mastoid specialization. Some of the Screw Bean taxa are late survivors of the Clarendonian Chronofauna, which extended through most or all of the early Hemphillian. The early early Hemphillian, late Miocene age attributed to the fauna is based on the Screw Bean assemblage postdating oreodont and predating North American edentate occurrences, on lack of defining Hemphillian taxa, and on stage of evolution.