Cataract Canyon heads at the confluence, but the rapids do not appear until we leave Spanish Bottom some 3½ miles below. Between The Loop and Spanish Bottom, the Colorado River follows closely the axis of an anticline. Along this reach the rock strata dip downward away from the river, as shown in [figure 61]. This fold was noted by Powell and some of his men, and Bishop (1947, p. 203) reported in his journal for September 16, 1871:
He [Steward] is at a loss how to account for the folded appearance of the strata here. But doubtless will find some explanation. Says the dip recedes from the river cañon, and thinks it is a fissure. Maj. [Powell] thinks it is owing to an upheaval, and that the beds next to the river have broken up from the mass, etc., etc.
Forty-four years later Harrison (1927) named this structure the Meander anticline and concluded that the weight of the rocks on each side of the river had squeezed underlying beds of salt in the Paradox Member of the Hermosa Formation and caused them to move upward along the river, where the confining strata had been removed by erosion. Harrison’s theory was accepted by Baker (1933) and most later workers in the area. Thus we have what may be termed an erosional anticline, whose axis, or crest, follows the river. Erosional anticlines also occur elsewhere, as along the Eagle and Roaring Fork valleys of central Colorado. Mutschler and Hite (1969) suggested that this zone of weakness in Canyonlands overlies and follows a break in the hard Precambrian ([fig. 80]) rocks that underlie the area at great depth. At any rate, Powell was on the right track even though he was totally unaware of the underlying salt or the deep-seated fault.
Smooth water continues from the confluence to Spanish Bottom, where the Old Spanish Trail comes down to the river from the west and continues up Lower Red Lake Canyon to the east. As mentioned earlier, this is about the south end of the Meander anticline, and an intruded chunk of the Paradox Member, mostly gypsum, occupies part of the mouth of Lower Red Lake Canyon, as shown in [figure 79].
The remaining 10 miles or so of Cataract Canyon within Canyonlands National Park contains many rapids and should be traversed only under the leadership of experienced river guides. If and when Lake Powell reaches its maximum level, it will extend to within about a mile of the park, but at present (1973) it heads near the mouth of Gypsum Canyon, about 5 miles below the park.
GYPSUM PLUG of Paradox Member, intruded along south end of Meander anticline at mouth of Lower Red Lake Canyon. Common salt has been removed by solution, leaving residue of gypsum and some shale. Photograph by Donald L. Baars. (Fig. 79)
GEOLOGIC TIME SPIRAL, showing the sequence, names, and ages of the geologic eras, periods, and epochs, and the evolution of plant and animal life on land and in the sea. The primitive animals that evolved in the sea during the vast Precambrian Era left few traces in the rocks because they had not developed hard parts such as shells, but hard shells or skeletal parts became abundant during and after the Paleozoic Era. (Fig. 80)