Lakes, like mountains, are temporary things. Even as lakes are forming, sediment begins to fill them until ultimately they are obliterated. So it was with Lake Uinta. Sometime after this lake dried up, the Earth’s crust again became restless. The gentle folds that were formed late in the Cretaceous were lifted higher and bent more sharply, and the flanks of some folds were wrinkled and broken (figs. [27], [28]). The sharply bent or broken rocks along the northeastern border of the Monument are thought to have been deformed mainly at this time, but in part both earlier and later. That pronounced folding of the rocks followed the deposition of the Eocene Green River Formation is clearly shown along the Grand Hogback monocline between the towns of Rifle and Meeker, Colorado, where the once flat lying beds of the Green River and Wasatch Formations now stand vertical.
The folds and faults along the northeastern border of the Monument, which are shown on the geologic map ([fig. 8]), are discussed briefly here—more details are given later in “Trips through and around the Monument.” The folded and faulted northeastern border of the Monument, which is shown in [figure 29] and in several ensuing photographs, is believed to have resulted from renewed uplift of the area southwest of the folds and faults, including the Monument. The Redlands fault (figs. [8], [29], [37], [38], [40], [41]) generally is a normal fault but locally is a reverse fault, as discussed on [page 92] and as shown in [figure 40] and in the cross section of [figure 8]. This fault has a maximum vertical displacement of 700 or 800 feet, but dies out in scissors fashion at each end. Beyond the end of the Redlands fault in the upper right of [figure 29] may be seen another unbroken monocline. A close-up view of the northwestern end of this fold in shown in [figure 30].
COMMON TYPES OF FAULTS. Top, normal, or gravity, fault which generally results from tension in and lengthening of a segment of the Earth’s crust, which allows the lower block to subside. However, some normal faults, particularly some that are vertical or nearly so, may result from uplift of the upper block. Low-angle reverse faults generally are called overthrust faults or simply overthrusts. In both the normal and reverse faults note amount of displacement and repetition of strata. Displacement of such faults may range from a few inches to many thousands of feet, and in overthrusts may reach many miles. From Hansen (1969, p. 116). (Fig. 28)
If we proceed about a quarter of a mile northeast of the point from which [figure 30] was taken, walk about 50 feet north, and look to the northwest, we see quite a different structure, for here the gentle lower fold of the Lizard Canyon monocline has become the east end of the Kodels Canyon fault ([fig. 31]).
LADDER CREEK MONOCLINE AND REDLANDS FAULT, telephoto view looking northwest from point near Little Park Road east of the Monument. No Thoroughfare Canyon in foreground, which is bordered on the left by northeastward-dipping beds of Wingate Sandstone at northwest end of Ladder Creek monocline. The old Serpents Trail, the lower part of which is barely visible, ascends this dipping block of rock. The dark Proterozoic rocks form the flat-topped bluff to the right and are exposed by the Redlands fault which lies just above the sharply upturned remnants of the Wingate Sandstone. (Fig. 29)
LIZARD CANYON MONOCLINE, looking southeastward across mouth of Lizard Canyon from southeasternmost loop of Rim Rock Drive just before it ascends Fruita Canyon. Note gentle lower bend at lower left and sharper upper one at upper right. Lower bend changes to Kodels Canyon fault in Fruita Canyon behind camera station. Grand Mesa forms left skyline. (Fig. 30)