The formation preserves fossils dating back to the Late Oligocene to Early Miocene (Arikareean in the NALMA classification).

The formation is the oldest non-marine unit of the Tejon region where the small Plush Ranch Basin is formed by the bounding Big Pine/Lockwood Valley and San Andreas Faults.

The unit is composed of alluvial and lacustrine conglomerates, sandstones, siltstones, shales, limestones, and evaporites.

Northwest of Plush Ranch Basin, on the opposite side of Mount Pinos (which includes exposures of Pelona Schist), Oligocene–Miocene strata are generally mapped as Simmler Formation, but are considered equivalent to the Plush Ranch Formation.

[1] The lacustrine deposits represent the central and eastern parts of the Plush Ranch basin, which received little coarse siliciclastic sediment.