The Sewellel has a thick, heavy body with short limbs. Body length is 33-47 cm. All of the limbs have 5 digits and those of the forefeet are fairly long since they are used for digging and grasping. It resembles a muskrat although it has no tail. The fur is short and dense with uniformly grayish or reddish brown coloring speckled with black. It has prehensile hands and feet.

It is most commonly found at lower elevations in forests and dense vegetation near waterways. Sewellels dig long burrows that are close to the surface which serve as shelter and a place to store food. It eats almost any plant material and drink large amounts of water.

They live alone or in loose colonies. It has a single yearly litter of 2-6 young.

They are found on the W coast of North America from SW British Columbia (Canada) to N California (USA), isolated populations in N and C California, extending into W Nevada.