Most people don't even know that the secretive, nocturnal creatures exist. Despite their common name, they are not beavers at all but share kinship with squirrels.
Fossils show that mountain beaver ancestors once ranged as far as Mongolia.
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.