The Pacific jumping mouse is a long tailed, sleek-bodied mouse. The pelage is course. The ocherous sides are separated sharply from the tawny dorsum; the venter is white, often washed with ochre. The tail is bicolored, but not markedly so.

In Oregon, the species occurs in the Cascade Range and westward to the Pacific Ocean except for southern Jackson County. These mice are largely marsh and meadow dwellers but are often found along creek banks or under ferns and weeds in the woods.

In September and October, these jumping mice become exceedingly fat; in captivity, they become progressively less active. In their hibernacula, they curl themselves into a tight ball, then wrap their long tails around their curled bodies.