Organic remains, especially dung, of extinct ground sloths provide ideal material for radiocarbon dating. Rampart Cave, Arizona, revealed periodic occupation at intervals by the Shasta ground sloth from before 40,000 years ago until 11,000 years ago. Dates from other caves in the arid Southwest indicate that the Shasta ground sloth disappeared at very soon after the time of Clovis big game hunters. Ground sloth remains in South America are slightly younger. The timing of ground sloth extinction is in accord with the model of explosive overkill.