Only since the last Ice Age ended has Aplodontia been restricted to the West Coast of North America. Today, seven subspecies are distributed along the moist coastal, coniferous belt that extends from southern British Columbia, through the western half of Washington and Oregon, into the Sierra Nevada and Coast Ranges of northern California. Their specialized physiology explains why their range is restricted to such a cool, stable, moist environment. Mountain beavers are unable to thermoregulate at high ambient temperatures and are susceptible to hypothermia. And their kidneys don't conserve water.
Mountain beavers produce nearly a third of their body weight in urine every day.
As a result, they cannot survive long without access to water or succulent vegetation. Since they cannot retain moisture or fat for winter hibernation or summer torpor, they consume a lot of food and water, mostly at night, within l00 feet of their burrows. At about l4 inches long, mountain beavers resemble overgrown pocket gophers without cheek pouches. Only a small, conspicuous white spot at the base of each ear breaks up their uniform color. Mountain beavers are built to dig.