Gopherus is a genus of fossorial tortoises commonly referred to as gopher tortoises. The gopher tortoise is grouped with land tortoises that originated 60 million years ago, in North America. A genetic study has shown that their closest relatives are in the Asian genus Manouria. The gopher tortoises live in the southern United States from California's Mojave Desert across to Florida, and in parts of northern Mexico. Gopher tortoises are so named because of their ability to dig large, deep burrows; those of the Gopher tortoise can be up to 40 feet (12 m) in length and 10 feet (3.0 m) in depth. These burrows are used by a variety of other species, including mammals, other reptiles, amphibians, and birds. Gopher tortoises are 20–50 cm (7.9–19.7 in) in length, depending on the species. All five species are found in xeric habitats.