The existence of a body of rock that is physically superposed above the type Heming-fordian Land Mammal Age but biostratigraphically below the type Barstovian Land Mammal Age justifies a redefinition of the Hemingfordian–Barstovian boundary. A new boundary stratotype is set at the base of the New Year Quarry in the Barstow Formation. New Year Quarry records the first appearance of gomphotheriid proboscideans in the Barstow Formation.
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Robert L. Evander (1986) studied this question.
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