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Figure 4. Deer Creek Falls (mile 136.1-R). .. A (left). September 10, 1923. Deer Creek Falls was photographed by every early river trip. This series shows the waterfall from river right on its debris fan. The large sandbar on the left side of the view is part of what attracted rivers to camp here (E.C. LaRue 547, courtesy of the U.S. Geological Survey Photographic Library). 8 (right). August 15, 1940. The annual flood of the Colorado River always reached the base of the waterfall, and the sandbar was annually renewed. The width of the waterfall changes as chock stones are added or removed from the slot. Although this photograph was taken from a different perspective than the 1923 view, new rocks are apparent on the debris fan (8.M. Goldwater, unnumbered, courtesy of the Center for Creative Photography, University of Arizona). he started working in Grand Canyon, and that subsequent floods constricted the river further. Rigg remembered small changes between 1959 and 1965 but thought the constriction was much worse now. Taken together, these observations indicate a typical pattern of several, closely-timed debris flows in one tributary, with little change before or after. The same course of events unfolded in other tributaries, including Prospect Canyon, where six debris flows and several other floods altered Lava Falls Rapid between 1939 and 1995. Dimock provided photographs and observations about the 1984 debris flow in Monument Creek (mile 93.5-L). His trip photographed an enormous wave that formed briefly just after the event. After successfully photographing (and running) the wave, Dimock said he never saw it or anything like it again in Granite Rapid. Dimock also noted changes on the left side of Soap Creek Rapid (mile 11.3; 1979-1982), which he attributed to a rockfall, and the reworking of the right side of House Rock Rapid (mile 16.9) by the 1983 flood. 14 OBSERVATIONS OF ENVIRONMENTAL CHANGE IN GRAND CANYON