The San Antonio Formation in California dates to the middle to late Pleistocene, within the Irvingtonian interval of the North American Land Mammal Ages. It is important as a fossil-bearing geologic unit that preserves evidence of ancient life from a time when California’s landscapes and climates were changing during the Ice Age. Its fossil record helps document prehistoric environments and animals across a broad span of Pleistocene time, and it is recognized as one of the state’s fossiliferous stratigraphic units.