Vegetation analysis of 47 Neotoma (packrat) middens from the core of the central Mojave Desert of California reveal changes in desert plant community composition over the last ca. 24,000 years BP, one of the lowest and most arid locations in North America. Habitat currently dominated by Mojave Desert Larrea tridentata (creosote bush) was occupied prior to ca. 11,500 years BP by Pinus monophylla (pin˜on), Juniperus osteosperma (Utah juniper), Purshia mexicana (bitterbush), Cercocarpus ledifolius (mountain mahogany), and Prunus fasciculata (desert almond) woodland above 1000 m. P. monophylla–Juniperus woodland was widespread over the southern and central Mojave Desert. However, less than 150 km north of the central Mojave, J. osteosperma steppe dominated the landscape. Paleoecologic records spanning latitude 358N ca. 378N document a biogeographic boundary between milder, moister environments to the south and the colder, drier environments to the north.
We have presented new information on vegetation development from the core of the Mojave Desert from the late Wisconsin to the present. A pronounced glacial- age paleoecotone spanned the north-central Mojave Desert, with mild-mesic woodland dominating inter- mediate elevations south of ca. 368N, and Juniperus- steppe vegetation occurring farther north. In the north, steppe shrubs were an important component of local vegetation at low elevations, to the south they were less frequent, and species such as Yucca whipplei occurred. Woodlands of the northern Mojave Desert contained only rare Pinus monophylla, while it appears to have been a common element of woodland vegetation at higher elevation Mojavean sites south of ca. 368N. The presence of P. monophylla in the Granite Mountains during the last glacial age supplements the late Wisconsin northern distribution of this species.