The desert tortoises (Gopherus agassizii and Gopherus morafkai) are species of tortoise native to the Mojave desert and Sonoran desert of the southwestern United States and northwestern Mexico and the Sinaloan thornscrub of northwestern Mexico. Gopherus agassizii is distributed in western Arizona, southeastern California, southern Nevada, and southwestern Utah. The species name agassizii is in honor of Swiss-American zoologist Jean Louis Rodolphe Agassiz. Recently, on the basis of DNA, geographic, and behavioral differences between desert tortoises east and west of the Colorado River, it was decided that two species of desert tortoises exist: the Agassiz's Desert Tortoise (Gopherus agassizii) and Morafka's Desert Tortoise (Gopherus morafkai). Gopherus morafkai occurs east of the Colorado River in Arizona as well as in the states of Sonora, Sinaloa, Mexico. This species may be a composite of two species.