Fig. 102. Forest road flooded by beavers which built a dam on the upstream (left) side of a bridge; Tronson Creek, Blewett Pass, Wenatchee National Forest, May 13, 1938. (Fish and Wildlife Service by Victor B. [Scheffer], No. 30.)
Probably the greatest value of beavers lies in the impounding of water by their dams. This is especially true in the arid mountains of eastern Washington and in the logged-off or burned-over parts of western Washington. These ponds prevent erosion, raise the water table and so stimulate the growth of vegetation, insure greater regularity of stream flow, provide suitable water for trout and muskrats as well as some breeding grounds for waterfowl. On burned-over or logged-off land, the greatest, and often the only, growth of new conifers is in the vicinity of beaver ponds. In the vicinity of beaver dams, rich growths of willows and other deciduous vegetation provides food and cover for deer and fur-bearing mammals.
Fig. 103. Distribution of the beaver in Washington. A. Castor canadensis leucodonta. B. Castor canadensis idoneus.
Trapping of beaver for their fur at present is not a private enterprise but controlled trapping by the state adds to public funds.