In 1955-56 the Arizona State Museum excavated an elephant-kill site on the Lehner ranch in the San Pedro valley, near Hereford, Arizona, and found 13 projectiles, mainly Clovis fluted points, eight butchering tools, and charcoal from two fires among the remains of nine immature mammoths and elements of horse, bison, and tapir. Bones and artifacts occurred on and in gravels of a former perennial stream exposed in the modern arroyo bank. Most or all of the animals were probably killed over a comparatively short period by hunters identified with the Llano complex by the Clovis points. The Lehner site and the nearby Naco site represent the southwesternmost extent of the presently known range of the Llano complex. The post-kill sequence of alluviation and erosion supports a geological age of 13,000 or more years for both bones and artifacts. Arizona, Michigan, and Copenhagen radiocarbon measurements of hearth charcoal indicate a date of 11,000 to 12,000 B.P. Since these dates are substantially older than the oldest radiocarbon assays for the Sulphur Spring stage of the Cochise culture, it is probable that the transition from big-game hunting to collecting is reflected in the change from Llano complex to Cochise culture, and that this shift in economic emphasis took place before the complete extinction of the late Pleistocene megafauna.