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~ 7 12 old, coarse- to medium-grained, pebbly, quartzitic sandstones (Fig. 3). The resistant nature of these strata is probably responsible for the canyon's characteristic straightness, depth, and narrowness. The canyon walls through this section are of high, blocky cliffs, usually reddish in color, and with talus slopes at river level. 2. Lodore Formation (Upper Cambrian) At approximately three miles above the confluence with the Yampa, the Green contacts this formation of ledgy sandstone interbedded with glauconitic, slope-forming shale. This contact lasts for less than three-quarters of a mile. For approximately one mile below the contact with the Lodore Formation, the Green contacts the Madison Limestone. Below this, it flows through the Mitten Park fault where the Humbug, Doughnut, Round Valley, and Morgan Formations are all exposed in a nearly vertical dip within a half mile. Weber sandstone Lines the last mile of the river above the confluence. The Green River from Echo Park through Split Mountain At F,cho Park, the Green River (now combined with the flow from the Yampa) makes a sharp bend to the north and again contacts the Mitten Park fault. It then turns to the west and enters Whirlpool Canyon. This canyon runs generally westward for 8.5 miles. The sinuosity is relatively low (1.17) and the average gradient is 12 f t./mile. The upper 1.5 miles of the canyon passes through sandstone of the Uinta Mountain group. The next 3.5 miles are through the Lodore Formation and the final 3.5 miles of river contacts in succession the Madison Limestone, Round Valley Formation, Morgan Formation, and Weber Sandstone.