Mammalian faunal remains recovered from three archaeological sites on the Oregon, U.S.A. coast provide strong evidence that 18th and 19th century commercial exploitation of marine mammals had major effects on the zoogeography and demography of those taxa. Zalophus californianus and Callorhinus ursinus bred and pupped along the Oregon coast between 3,000 and 100 yr ago. About 100 yr ago Eumetopias jubatus abandoned a major rookery that had been utilized since at least 400 yr ago. Phoca vitulina does not appear to have suffered major modifications to coastal use or demographic patterns in Oregon during the last 3,000 yr, although a minor incident of intensified utilization of one location about 1,000 yr ago is suggested. All age-sex classes of Enhydra lutris lived on the Oregon coast until about A.D. 1900. Oregon's prehistoric remains of E. lutris display some dental characters similar to modern Alaskan specimens, and other dental characters similar to modern Californian specimens, conforming to a latitudinal dine reflected by historic specimens. Additional evidence for many of these observations is found in faunal remains recovered from archaeological sites on the coast of Vancouver Island, the Washington coast, and the northern California coast.