The Barstow Formation is a series of limestones, conglomerates, sandstones, siltstones and shales exposed in the Mojave Desert near Barstow in San Bernardino County, California. It is of the early to middle Miocene epoch, (19.3 - 13.4 million years ago) in age, in the Neogene Period. It lends its name to the Barstovian North American land mammal age (NALMA).