This mouse lives in saline and brackish wetlands around San Francisco Bay. Its back is dark brown, while reddish bellies vary by location.
Its back is rich brown and the tail may be one- or two-toned. Reddish or cinnamon bellies occur only in some populations of the southern subspecies.
It is mostly active at night, though it is also active by day on warm days. It eats leaves, seeds, and stems, and favors pickleweed and saltgrass in marshes.
An extinction-risk assessment has not been added yet.