The Pacific shrew is the only shrew in Oregon without a tine on the anteromedial surface of the first upper incisor but with a posteriomedial ridge visible in anterior view through the gap between the incisors. It is a large brown shrew with the third unicuspid smaller than the fourth.

The species is often found in moist wooded areas with fallen decaying logs and brushy vegetation. It is endemic to Oregon and is distributed as two disjunct populations: one in the Coast Range from Cascade Head, Tillamook County, south to Coos Bay, Coos County and eastward to Philomath, Benton County and Sutherlin, Douglas county; the other in the Cascade Range from northeastern Linn County to southern Jackson County.