A 33,000 yr pollen record from Carp Lake provides information on the vegetation history of the forest/steppe border in the southwestern Columbia Basin. The site is located in the Pinus ponderosa Zone but through much of late Quaternary time the area
of rapid climatic amelioration. In the early Holocene, the prolonged expansion of Pseudotsuga and Alnus woodland suggests dry, temperate conditions similar to those of present rainshadow sites in the Puget Lowland. More-mesic forests of Tsuga heterophylla