| This dissertation presents a coordinated sequence of analyses, based on entirely new modern and fossil pollen data, which results in paleoclimate and paleovegetation reconstructions in the montane region of Southern California throughout the Holocene (approximately the last 11,500 years). The pattern of this sequence of analyses is: (a) a modern pollen surface sample reference set in the region which relates modern pollen representation to climate and regional vegetation; (b) examination of the optimal threshold for determining significant likeness between pollen samples from similar vegetation in the region, for use in the Modern Analog Technique (MAT); (c) calibration and testing of the MAT methodology used for reconstructing paleoclimate; (d) reconstruction of paleoclimate and paleovegetation, based on MAT comparison of the fossil pollen record with the modern reference set. The results of this research indicate that the climate and vegetation of the Southern California montane region east of Los Angeles and San Diego have been relatively unchanged over the last 11,000 years, with significant cooling in the period just after the end of the Younger Dryas episode (approximately 10,800–11,500 years ago). This record differs significantly with that from a lowland site just west of the mountain foothills in the early Holocene and with the early-Holocene record from the Sierra Nevada Mountains in Central and Northern California, both of which indicate significantly drier-than-present conditions. These differences are consistent with paleoclimate simulations from atmospheric general circulation models, which indicate a significantly enhanced summer monsoon in the American Southwest at this time. The evidence from this dissertation suggests that this circulation pattern also affected at least the eastern and southern portions of the Southern California mountains, but did not affect the west-of-the-mountain lowlands and the Sierra Nevada further to the northwest. |
