There is only one species in this family. The mountain beaver (Aplodontia rufa) is found in forests in the Pacific Northwest from British Columbia to central California.

It is not really a beaver, and it doesn’t only live in the mountains. Scientists believe that the mountain beaver is the world’s most primitive living rodent species.

The mountain beaver looks like a woodchuck. It has dark brown fur on its uppersides, grayish-brown fur on its undersides, and a white spot under its ears. It has a stocky body, a wide, flat head, a short, stubby tail, and short legs with clawed feet.

Mountain beavers live in burrows with more than one opening. They have separate chambers in their burrow for nesting, food storage, and waste.

Mountain beavers eat grasses, ferns, and bark. They have very small kidneys and must drink at least 1-2 cups of water a day. Because they need so much water, they always live near a water source.

Except during the breeding season, the mountain beaver is a solitary animal.