Barstovian Stage, uppermost major division of the Miocene Epoch (23 million to 5.3 million years ago) in North America. The Barstovian Stage follows the Hemingfordian Stage and precedes the Clarendonian Stage of the Pliocene Epoch. It was named for exposures studied near Barstow, Calif. The Barstovian contains a distinctive mammalian fauna.