Beaver (Castor canadensis) populations of the Pacific Northwest interior underwent a drastic decline from 1835 to 1850, as evidenced by a steady decrease in harvest. There is little evidence that price changes, company trapping policy, losses to rival traders, or social upheaval had a significant effect on the returns from the upper Columbia River basin. The proportion of juveniles increased in harvests from exploited populations because of (1) changes in age structure, (2) reduced trappability of the older age groups, or (3) both of these factors. Certain populations showed evidence of recovery beginning about 1850.