The Mojave Desert, which lies between the Great Basin Desert in the north and the Sonoran Desert in the south, covers an estimated 114 478–130 464 km² of the south-western United States and includes parts of the states of Nevada, Utah, Arizona, and California, with the amount of land mass dependent on the definition (Fig. 1; Rowlands et al., 1982; McNab and Avers, 1994; Bailey, 1995; Groves et al., 2000). This desert is sufficiently diverse to be subdivided into five regions: northern, south-western, central, south-central, and eastern (Rowlands et al., 1982). It is a land of extremes both in topography and climate. Elevations range from below sea level at Death Valley National Park to 3633 m on Mt. Charleston in the Spring Range of Nevada. Temperatures exhibit similar extreme ranges with mean minimum January temperatures of −2.4 °C in Beatty, Nevada and mean maximum July temperatures of 47 °C in Death Valley. Mean annual precipitation varies throughout the regions (42–350 mm), is highest on mountain tops, but overall is low (Rowlands et al., 1982; Rowlands, 1995a). The distribution of precipitation varies from west to east and north to south, with >85% of rain falling in winter in the northern, south-western and south-central regions. In contrast, the central and eastern regions receive a substantial amount of precipitation in both winter and summer. The variability in topographic and climatic features contributes to regional differences in vegetation.