The Diligencia Formation (Td) is a geologic formation cropping out in the Orocopia Mountains in southern California.

It preserves mammal fossils dating to the Late Oligocene to Early Miocene (Arikareean in the NALMA classification).

[1] The non-marine Diligencia Formation, defined by Crowell in 1975, is composed of alluvial, fluvial, and lacustrine conglomerates, sandstones, siltstones and limestones.

It contains interbedded basalt and andesite flows, dated by whole-rock and plagioclase K-Ar methods as ca.

24–21 Ma), and andesitic sills and dikes.