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]

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Diligencia Formation
Stratigraphic range: Late Oligocene-Early Miocene (Arikareean) ~25–20.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Formation
Overlies	Proterozoic augen gneiss (basement) Maniobra Formation (in the north)
Thickness	1,500 m (4,900 ft)
Lithology
Primary	Conglomerate, sandstone, siltstone, limestone
Other	Interbedded basalt and andesite
Location
Coordinates	33.5°N 115.7°W / 33.5; -115.7
Approximate paleocoordinates	32.2°N 107.5°W / 32.2; -107.5
Region	California
Country	United States
Extent	Orocopia Mountains
Type section
Named by	Crowell
Year defined	1975
Diligencia Formation (the United States) Show map of the United States Diligencia Formation (California) Show map of California

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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.^[2][3]

The formation has provided the following fossils:^[1]

Mammals

• Artiodactyls
  • Merycoidodontidae
    • Merychyus cf. minimus^[4]