The Arizona transition zone is a diagonal northwest-by-southeast region across central Arizona. The region is a transition from the higher-elevation Colorado Plateau in Northeast Arizona and the Basin and Range region of lower-elevation deserts in the southwest and south.
Northwest Arizona transitions to the lower elevation Mojave Desert of southern California, Nevada and Utah, with an indicator species of Joshua trees and other species, and southwestwards regions of the Sonoran Desert, along the Lower Colorado River Valley; in Arizona's south, all of central and eastern desert Sonoran Desert regions merge southwards into Sonora Mexico. The transition zone includes the Mogollon Rim and the White Mountains and extends into western New Mexico.
In the Arizona ecoregion section, the Arizona transition zone is the major section of the EPA designated, Level III ecoregion, Arizona/New Mexico Mountains ecoregion. The other two outlier subregions to the transition zone in Arizona, are the Kaibab Plateau of the North Rim of the Grand Canyon, and associated ranges of the Chuska Mountains region of the northeast Arizona and northwest New Mexico.
