LATE WISCONSIN EARLY HOLOCENE VEGETATION IN THE BONNEVILLE BASIN

Woodrat middens from the northern Bonneville Basin allow a reconstruction of vegetation changes from 14,000 to 9000 gr ago. Cold montane steppe, dominated by sagebrush, covered much of the western Bonneville Basin prior to 13,000 yr ago. From 13,000-10,800 yr ago, the region was vegetated by limber pine woodlands in lower montane settings and a mosaic of limber pine and sagebrush steppe along basin floor margins. These low-elevation timber pine woodlands began to retreat upslope after about 11,000 yr ago due to increasingly drier climatic conditions, and were replaced by relatively more xeric desert scrub dominated by sagebrush and shadscale. The growth of limber pine at low elevations suggests that summer temperatures were as much as 6 degrees C tower than at present, This evidence is in apparent conflict with the currently accepted post-Prove Lake Bonneville chronology, especially the magnitude of the postulated near-dessication of Lake Bonneville from ca. 13,000-12,200 yr ago. (C) 1995 University of Washington.