| OCR Text |
Show invisible from the ground, but clearly evident on aerial photographs) indicate that the upper Provo River was once a northward- flowing stream. At what time the stream changed its course is not know, but it was probably near the end of Pleistocene time, as the lithology and sorting of the alluvial fill near Francis suggest that the material was derived largely from glacial action in the mountains. Why the stream's course was changed is a more difficult question, but two hypotheses have been suggested. 1. The northern outlet from Rhodes Valley was blocked, and the ponded water rose until it could find an outlet through a pass in the hills on the west side of the valley. Erosion subsequently lowered the outlet to form the narrow upper Provo Canyon. 2. The east fork of the original Provo River ( that is, the lower stream), working on a high gradient, lengthened its course by headward erosion and cut through the low divide, thus intercepting and capturing the upper river. Either of these hypotheses seems to require the presence of a zone of weakness, probably structurally controlled, to permit the carving of the upper Provo Canyon through the hard volcanic rocks in a relatively short time. The writer prefers the second hypothesis, despite the obvious difficulty of rapid headward erosion of a small stream through hard rocks, for the following reasons: 1. The first hypothesis requires ponding of water in Rhodes Valley, and no evidence of such ponding has been found. 2. If the northern outlet of Rhodes Valley were blocked, then when the postulated pond was drained through upper Provo Canyon the Weber River and Beaver Creek should have joined the upper Provo River, but both these streams still flow northward. Tributaries, reservoirs, and diversions The main stem of the Provo River heads in a cluster of rock- basin lakes near the crest of the Uinta Mountains. North Fork, the only large tributary that enters the river from the north, also heads in a group of small lakes near the crest of the range. Soapstone Creek, South Fork, and Little South Fork drain a part of the Rhodes Plateau ( fig. 1), which separates the drainage of the Provo River from that of the Duchesne River. All these tributaries enter the Provo River above the gaging station near Woodland, and there are no perennial tributaries between the gaging station and Hailstone. Drain Tunnel Creek ( Ross Creek) enters the Provo River near Hailstone. The creek is intermittent upstream from the mouth of the Ontario No. 2 Drain Tunnel, and it is unlikely that there would be perennial surface inflow to the river without the discharge of the tunnel. Lake, Center, and Daniels Creeks drain the Rhodes Plateau. The flow of Lake and Center Creeks is now directed to Daniels Creek; Daniels Creek discharges to Deer Creek Reservoir. Snake Creek and its tributary, Pine Creek, are the only perennial streams that flow from the Wasatch Range to the Provo River above Deer Creek Reservoir. Two small tributaries, Rock and Spring Creeks, originate from ground- water discharge in Heber Valley. 7 |
