<P> The desert tortoises live about 50 to 80 years; they grow slowly and generally have low reproductive rates . They spend most of their time in burrows, rock shelters, and pallets to regulate body temperature and reduce water loss . They are most active after seasonal rains and are inactive during most of the year . This inactivity helps reduce water loss during hot periods, whereas winter hibernation facilitates survival during freezing temperatures and low food availability . Desert tortoises can tolerate water, salt, and energy imbalances on a daily basis, which increases their lifespans . </P> <P> These tortoises may attain a length of 10 to 14 in (25 to 36 cm), with males being slightly larger than females . A male tortoise has a longer gular horn than a female, his plastron (lower shell) is concave compared to a female tortoise . Males have larger tails than females do . Their shells are high - domed, and greenish - tan to dark brown in color . Desert tortoises can grow to 4--6 in (10--15 cm) in height . They can range in weight from . 02 to 5 kg (0.044 to 11.023 lb). The front limbs have sharp, claw - like scales and are flattened for digging . Back legs are skinnier and very long . </P> <P> Desert tortoises can live in areas with ground temperatures exceeding 140 ° F (60 ° C) because of their ability to dig underground burrows and escape the heat . At least 95% of their lives are spent in burrows . There, they are also protected from freezing winter weather while dormant, from November through February or March . Within their burrows, these tortoises create a subterranean environment that can be beneficial to other reptiles, mammals, birds, and invertebrates . </P> <P> Scientists have divided the desert tortoise into two types: Agassiz's and Morafka's desert tortoises, with a possible third type in northern Sinaloan and southern Sonora, Mexico . An isolated population of Agassiz's desert tortoise occurs in the Black Mountains of northwestern Arizona . They live in a different type of habitat, from sandy flats to rocky foothills . They have a strong proclivity in the Mojave Desert for alluvial fans, washes, and canyons where more suitable soils for den construction might be found . They range from near sea level to around 3,500 feet (1,100 m) in elevation . Tortoises show very strong site fidelity, and have well - established home ranges where they know where their food, water, and mineral resources are . </P>

What protects the north american desert tortoise from heat