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GEOMORPHIC EFFECTS OF THE FLOOD 33 FIGURE 24.-Elkhom Avenue, Estes Park, looking downstream from river mile 12.0 (aerial). Big Thompson River is along the right side of the photograph; Lake Estes is in the top righthand corner. Photo courtesy of Zenas Blevins, U.S. Bureau of Reclamation. coured reaches, very large boulders in ground moraine rere undercut and had simply fallen onto the channel loor. The criteria used to establish that a particular IOU!.der did, in fact, move in the flood were: (1) Percus- ion marks on all sides of the boulder, not just on the lpstream side; (21 balanced and wedgedsma1ler rocks, end broken and buried vegetation under larger boulders; end (31 boulder clusters and berms in streamlined deposi- ional forms, with imbricated structure parallel to the low direction (fig. 301. Some of the largest measured IOUlders known to have been moved in the Roaring River ralley have dimensions of 5.5X8X12.5 ft, 7X12X13 ft, Illd 3X7X8 ft. Larger boulders were observed in the :hannel, but minimal or no evidence existed to indicate hat they had been moved by the dam-failure flood. Much less conspicuous. but nevertheless ubiquitous, ~ere sand deposits. Sands were deposited almost :ontinuously, away from the main flood channel, within ;he edge of the surviving forest and vegetated areas on he valley sides below high-water marks. Some sand ieposits were 4 ft thick and had steep wave fronts ;acing downstream (fig. 311. Sand deposits along the Roaring River are very coarse and massive. or have weak horizontal laminations (fig. 32). About 400 ft downstream from the Lawn Lake dam, sand splays are extensively developed on the right bank. High-water marks indicated the flood flow was 3.5 ft deep over the top of these splays. Along the edge of the splay next to the deeply eroded channel, back set beds. interpreted to be antidune structures, were preserved (fig. 331. These backset beds were diffuse, curved, and TABLE 7-Clumnel conditions, Roaring River DbtaDc:e dowDatream from lAwn Lake dam. A__ c__ iDmiln mperctllt """"""'. Below 1.... Lake clam 0.00-0.24 7.5 scour .24- .68 6.9 deposition .68-1.00 25 scour 1.00-1.16 9.2 deposition 1.16-1.49 23.5 scour 1.49-1.70 5 daposition 1.70-1.95 13.3 scour 1.95-2.23 5.5 deposition 2.23-2.74 7.1 scour 2.74-3.62 5.7 deposition Honesboe FaII& 3.62-4.02 26 scour 31