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Figure 3. The sand bar downstream from Tapeats reek (mile 133.9-R). A. July 1952. This view downstream from the below he mouth of Tapeats Creek (mile 133.8-R) shows a large sand bar with few rocks or boulders exposed. This s nd bar was frequently used for layovers in the 1950s; the passengers of Mexican Hat Expeditions trips fished or trout in the creek (Kent Frost, no number, courtesy of the photographer). Luepke and Euler, had suggested that the initial phase debris flow using matched photographs from 1890 and of the flood was a debris flow because of the new those of Goldwater (1940) and Bill Fahrni (1934). The debris fan that was created. We already knew that year of the debris flow causing the change is still changes in the debris fan under the Silver Bridge were unknown, but it occurred between 1940 and 1965. among the most extensive of the last century in Grand The Old Timers have contributed greatly to our Canyon, but Litton and Cross II reinforced the knowledge of debris-flow frequency with their hypothesis that the early stage of the 1966 flood was a photographs and memories. For example, Nichols debris flow followed by higher flood waters bearing consistently took photographs of Badger Creek Rapid less sediment. Melis and others (1997), have reported from the left canyon rim. His photographs document that such multi-phased floods, starting as a debris flow changes in the sand bars and tamarisk and provides the and ending with intense streamflow, are common in basis for determining whether any debris flows had Grand Canyon tributaries. The 1995 Bright Angel occurred prior to one in August 1994 (Melis, 1997; Creek debris flow had a similar effect on the river and Melis and others, 1994). We also used many of Reilly's f left similar evidence. photographs to document debris-flow frequency in Most of the Old Timers, particularly Jones, were Grand Canyon, particularly at Lava Falls Rapid (Webb impressed by the large number of recent debris-flow and others, 1999b). deposits along the river. Some Old Timers did not The Old Timers recognized the large change at remember evidence of debris flows specifically, but the mouth of Tapeats Creek, where many of them had they recognized small changes in places they had spent considerable time. The channel mouth shifted previously visited. Frost knew that the mouth of South upstream during a 1961 flood. They also noticed the Canyon (mile 31.6-R) had changed since his last visit. large decrease in sand present (see below), which in We previously had documented the occurrence of the part was related to channel change at the mouth. The 12 OBSERVATIONS OF ENVIRONMENTAL CHANGE IN GRAND CANYON