Mountain beaver, also called sewellel, is a rodent that lives along the Pacific coast and in nearby mountains. Mountain beavers, which are not related to true beavers, have lived on Earth longer than any other rodent. They lived in North America at least 60 million years ago. They are also called boomers and whistlers, though they do not make booming or whistling noises. Sewellel is a Chinook word meaning robe. 
Mountain beavers are about 1 foot (30 centimeters) long and look like large voles rather than like beavers. They have a short, thick body, short legs, a short tail, and small eyes and ears. Their fur is thick and short. Mountain beavers live in groups called colonies. They live in tunnels they dig in the banks of streams.
