Compact, heavyset, water mammal with brown fur and a broad,
horizontally-flattened, scaly tail. Large, webbed hind feet. Total
length about 3½ feet. Average weight about 40 pounds. When swimming,
only the top half of the head, shoulders, and part of the back appear
above water. For positive identification, watch for the broad, black
tail which may slap the water, or "flip up" when it dives.
This largest of North American rodents is very abundant and widely
distributed in many of the mountain streams. To locate their dams, look
for small pools or lakes in streams of heavily wooded sections. If new,
the dams will be a mass of twigs and saplings carefully interlaced and
sealed with mud; if old, the dams will be overgrown with grasses and
small shrubs, but will still maintain the general shape and contour of a
beaver dam. These dams will easily support the weight of a man. In the
pond area or on the dam, a conical mass of mud and twigs, (the beaver
lodge) some three to five feet high may be found, which contains the
home of the beavers using that pond. Each lodge has an underwater
entrance which is constantly in use, winter and summer. While beavers
work mostly at night, it has been a regular practice in the Park to
observe them swimming in their ponds just before nightfall. The Mill
Creek, Hidden Valley, and Colorado River Valley areas have been
especially good locations for sight of beaver. If aspen, which is both
the beaver's food and construction material, have all been removed for a
distance of five or six hundred feet from the pond, then probably the
beavers have moved out and gone up or down stream to build a new pond.
Muskrats may then occupy the entire pond.