RELATIVELY RECENT RINCONS ALONG INDIAN CREEK, about 3½ miles above mouth and about 2 miles east of Canyonlands National Park. Above, stereoscopic pair of aerial photographs by U.S. Geological Survey; below, sketch showing drainage changes. The stereoscopic pair can be viewed without optical aids by those accustomed to this procedure, or by use of a simple double-lens stereoscope. (Fig. 73)
THE LOOP, of Colorado River, about 5 miles northeast of the confluence. Lower canyon walls are unnamed upper member of Hermosa Formation overlain by slopes of the Rico Formation. Jointed sandy ledges at top become sandier to south, where they comprise the Cedar Mesa Sandstone. Aerial photograph by U.S. Geological Survey. (Fig. 74)
About 5 miles below the mouth of Rustler Canyon and Indian Creek, and also about 5 miles above the confluence, is The Loop—an even sharper and more symmetrical figure eight than Bowknot Bend of the Green River ([fig. 62]). An aerial view of The Loop ([fig. 74]) shows that the channels on the south loop are only about 500 feet apart and that those on the north loop are only about 1,700 feet apart. At the narrowest places, both saddles are considerably eroded—the southern one is only about 150 feet above the river, but the northern one is still about 350 feet above. Erosion of both saddles has been hastened by the facts that the axis of the Meander anticline (see [p. 108]) passes through each saddle and that an interesting reverse fault ([fig. 75]) passes through the lower and thinner southern saddle. The differences between reverse and normal faults are shown by comparing figures [56] and [76]. It seems inevitable that some day the small saddle will be cut through by the Colorado River, and a new rincon will result. Eventually, the other loop also probably will be abandoned. As one of my colleagues remarked, how wonderful it would seem, to be present at the proper moment to witness such an event, particularly if one had a time-lapse movie camera to record it for posterity!
REVERSE FAULT in southern saddle of The Loop, looking northwest from boat in river. Apparent angle of dip is 12° below horizontal. Rocks at left, above fault plane, have been shoved about 10 feet past and over those on right. Curving of dark bed near middle of fault plane is called “drag.” (See [fig. 76].) Rocks are unnamed upper member of Hermosa Formation. (Fig. 75)
CUTAWAY VIEW OF REVERSE FAULT, resulting from horizontal compression, which caused a shortening of earth’s crust. Note “drag” of beds on each side of fault plane. Low-angle reverse faults, also called thrust faults, may have displacements ranging from a few feet to many miles. From Hansen (1969, p. 116). (Fig. 76)