In 1935 Quaintance and White spent June 16 to June 20 in the Mancos
River Bottoms at the mouth of Weber Canyon, looking for sign of fresh
beaver work. They found none. Annual Animal Census Reports include the
following information based on patrols along the Mancos River at the
east boundary of the Park: 1937--estimate 4 beaver present, 1938--8,
1941--numerous bank burrows, 1942--uncommon, 1944--uncommon, 1945--most
concentrated at southeast corner, 1946--runs and two small dams seen
(flood had washed out larger dams), 1947--only in 1-1/2 miles north of
boundary with Ute Reservation, 1949--two separate colonies (each with
dams and one with a large house), 1950--none, owing to drouth and
diversion of water upstream completely drying the river at times,
1951--none, 1953--present, 1955--present. On the Mancos River, 6200 ft.,
in late August, 1956, sign of beaver was abundant, numerous trees had
been cut but none within a week, and a bank den was found on the west
side of the river extending back 50 feet from the stream and caved in at
three places. In 1959 dens were still present.