Since the discovery 15 years ago by Sears and Clisby that the dry lakes (playa lakes) of western North America contain a rich fossil pollen record, Pleistocene specialists have hoped that a definitive chronology would be forthcoming from this largely unglaciated region. Such a chronology should indicate the number of pluvial episodes and the magnitude of each. The deepest drill cores should reveal whether the Pleistocene began with a "bang" or a "whimper."

Though hopes for a continuous Pleistocene chronology go largely unrealized, the pollen record of the last glacio-pluvial maximum, the Wisconsin, is increasingly well known. It indicates a major shift in vegetation zones not once but several times during the C-14-datable part of the record. Among the areas studied to date are the San Augustin Plains, the Willcox Playa, Great Salt Lake Desert, and the Texas High Plains. Some control on the fossil pollen record can be gained from the modern pollen rain of "natural" plant communities in the southwest. Despite formidable problems of long-distance transport of certain pollen types it appears that the major vegetation zones have their own distinctive local pollen pool,

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making it possible to interpret Pleistocene vegetation history, at least in rough terms. The results are best illustrated in a Pleistocene full-glacial vegetation map.

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