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<br />FLOODS OF SEPT. 1970 IN ARIZ., UTAH, COLO., AND N. MEX.
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<br />:roded, and trees, brush, and boulder bars were removed by the tremendous
<br />.orce of the water. Because the flow swirled unevenly around bends and
<br />:purs, the heights of the fl06dmarks on opposite banks differed by as much
<br />,s 16 ft (4.9 m). The mudflow that occurred after the peak left a trail of mud,
<br />:and, and pebbles on the sides of the channel, on boulders, and ona few logs
<br />'ar below the floodmarks. The mudflow merged with the floodwater from
<br />ronto Creek, and did not extend downstream from the confluence of Dick
<br />Williams and T onto Creeks.
<br />The flood demolished a bridge and damaged several cabins along Tonto
<br />:::reek downstream from Dick Williams Creek; refrigerators and other
<br />lOuse hold items were carried more than 1 mi (1.6 km) downstream. Two
<br />,eople were killed when a cabin was carried away by floodwater. According
<br />o eyewitness reports, high-velocity flow in the center of the channel created
<br />, dome of water that was several feet higher than the water near the edges of
<br />:he channel. An enormous boulder-about 7 by 9 by 4 ft (2.1 by 2.7 by 1.2
<br />m)-was rolled by the flood and perched spectacularly on top of logs
<br />.gainst a ponderosa pine tree growing in the middle of the channel (fig. 9).
<br />The base of the boulder was 16 ft (4.9 m)above the channel bottom, which is
<br />nearly the same height as the floodmarks on the banks. Bark was removed on
<br />the upstream side of the pine tree to a height of24 ft(7.3 m), which indicates
<br />that the water in the middle of the channel was 8 ft (2.4 m) higher than it was
<br />near the edges of the channel. Sandstone fragments embedded in ponderosa
<br />pine logs, as if they had been shot as projectiles, illustrate the high velocity of
<br />the flow; more than 15 fragments were counted in a 12-ft (3.7-m) length of a
<br />3-ft-diameter (0.9-m-diameter) log.
<br />The greatest single tragedy of the flood of 1970 took place at the bridge
<br />over Tonto Creek just downstream from the confluence of Tonto and
<br />Horton Creeks during the late afternoon of September 5. According to W. L.
<br />Buckner (U.S. Forest Service Ranger, oral commun., 1970), some of the logs
<br />md trees transported .by Tonto Creek accumulated upstream from the
<br />bridge abutments and caused a tremendous amount of splash over the railing
<br />of the bridge. Two cars were parked on the west approach within50ft(I5 m)
<br />of the bridge. Suddenly, a wall of water 4-5 ft (1.2-1.5 m) high was diverted
<br />by the debris that had collected upstream from the bridge. The water washed
<br />away the cars, and the 12 occupants were drowned. The flood eventually cut
<br />. channel through the west approach to the bridge and gouged out a large
<br />,ection of the adjoining terrace. The peak flow covered nearly all the terrace,
<br />which is 15 ft (4.6 m) above the streambed nearthe bridge, and deposited a
<br />mantle of logs about 8 ft (2.4 m) deep over an area 200 by 200 ft (60 by 60 m)
<br />on the part of the terrace nearest the bridge.
<br />In the Kohl Ranch area many houses and cabins are built on a fairly
<br />continuous terrace about 11-14 ft (3.4-4.3 m) above the bed ofTonto Creek.
<br />The flood inundated the lower part of the terrace and damaged buildings; the
<br />buildings, trailers, and roads on the slopes below the terrace were severely
<br />damaged (fig. 10).
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<br />CENTRAL ARIZONA
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<br />FIGURE 9.-A flood--deposited boulder perched on top of logs in upper Tonto Creek.
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<br />According to a resident (H. P. Walker, oral commun., 1970), the flood of
<br />1970 was the largest known in Christopher Creek-a small east tributary to
<br />Tonto Creek. At the Mountain Meadow Ranch about I mi (1.6 km)
<br />upstream from State Highway 160, the creek suddenly rose 3-4 ft (0.9-1.2 m)
<br />after it had been running bankfull. Large trees as much as 4 ft (1.2 m) in
<br />diameter and 100 ft (30 m) long formed logjams and covered an area about
<br />700 ft (210 m) long upstream from the ranch. Cabins at the ranch were
<br />inundated by as much as 2 ft (0.6 m) of water; the logjams spread the flow of
<br />the creek over the entire area, which probably saved the cabins from the
<br />more severe damage that would have resulted from higher velocity flows.
<br />According to H. P.W alker (oral commun.; 1970), the channel of Christopher
<br />Creek at the intake ofa diversion ditch built in 1890 was downcut4 ft (1.2 m),
<br />which was the first major downcutting since the ditch was constructed. At
<br />Christopher Ranch downstream from State Highway 160, most of the cabins
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