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Figure 2. Badger Creek Rapid (mile 8.0)(continued). .. B. October 1968. Nichols approximately matched his earlier photograph and documents an increase in the sand bars and tamarisk growth. The increased sand likely was deposited during the summer 1965, high releases from Glen Canyon Dam. The rapid is unchanged (Tad Nichols, no number, courtesy of the photographer). gravel on his trip in early October 1963; it made his portage of Lava Falls Rapid much easier. Our photographic evidence of this debris flow suggested that it occurred between August and September 22, 1963; Jones' recollection corroborates our independent estimate. The occurrence of five of the six debris flows at Prospect Canyon in the 20th century were known only from photographs taken by river runners or scattered observations. The movies and photographs taken during Harris' trip in July 1939 show what Lava Falls Rapid looked like before the September 1939 debris flow, which was the largest of the 20th century (Webb and others, 1999b). Reilly's photographs span the three debris flows of 1954, 1955, and 1963. He observed the effects of the debris flow of 1955 in Prospect Canyon (mile 179.4-L) and wrote that the 1956 high water had sliced into the newly deposited debris fan, leaving a 15- foot-high bank. This observation was verified in Nichols' photographs, which show the boats of a Mexican Hat Expeditions trip being portaged over that bank. Finally, during an August 1967 trip with Georgie White, passenger Gretchen Luepke photographed the 1966 debris-flow deposits at both Lava Falls Rapid (mile 179.5) and Bright Angel Creek (mile 87.8-R). Her photographs verify what John Cross II observed in March 1967 on the first trip to experience Lava Falls after the 1966 debris flow. Other river runners did not observe or did not choose to record debris-flow deposits. Frank Wright wrote detailed trip logs (Table 1), yet he failed to record either the Boucher Creek deposition or th~ two debris flows at Prospect Canyon, despite the fact that others on his trip either remembered them, wrote about them, or photographed them. P. T. Reilly meticulously noted the signs of recent flooding in tributary canyons. Most of what he observed can be attributed to streamflow floods, not debris flows. He observed new mud and silt in the mouth of Shinumo Creek (mile 108.6-R) in 1949. In ~ 10 OBSERVATIONS OF ENVIRONMENTAL CHANGE IN GRAND CANYON