The late Pliocene basal clay of the region and remnants of later deposits are cut by a perennial stream of pluvial age. Bones and artifacts, including Clovis- fluted points, occur in gravel and other channel deposits in a meander bow of this stream. The bone bed is overlain by a black swamp deposit indicating a subhumid climate and by calichified silts indicating arid conditions, both cut by an Altithermal channel. The hunt, stratigraphically pre- Altithermal, is dated by the equation of the relatively warm and dry 14-to-12 foot level in the San Augustin Plains profile with the Allerod of northern Europe (12,500-10,800 B.P.). This semi-arid period, called the Datil Interval or Datil Drought, is believed to have caused the extinction of the mammoth in both the Southwest and the High Plains by 11,500 B.P. The Sulphur Spring stage Cochise deposit at Double Adobe, which is overlain by a bed containing a mammoth skull, is dated at more than 12,500 B.P. The mammoth hunts of the Lehner and Naco sites are assigned an age of 13,000 or more years.