[Illustration: PROBABLE STEPS IN FORMATION OF POTHOLE ARCH. _A_, Original pothole probably formed in relatively level bed of sandstone, such as this one, which is in an older rock unit—the White Rim Sandstone Member of the Cutler Formation, a unit not present in Arches. This pothole, which contains 4 feet of water, is in nearby Canyonlands National Park (Lohman, 1974, fig. 17), just north of the edge of the White Rim, about 4½ miles north of the confluence of the Green and Colorado Rivers. Photograph by E. N. Hinrichs. _B_, Pothole is being deepened by solution while cliff is receding toward pothole by weathering. _C_, As erosion continues, pothole and cave in cliff face are growing deeper. _D_, Pothole Arch formed by union of vertical pothole and horizontal cave. _E_, Telephoto view of Pothole Arch from park road near stop 14. Visible span is 90 feet across and 30 feet high. (Fig. 18)] [Illustration: Fig. 18 B] [Illustration: Fig. 18 C] [Illustration: Fig. 18 D] [Illustration: Fig. 18 E] The cause of the wavy bedding in the Dewey Bridge Member, as shown in figure 17 but as better shown in the frontispiece, is not known for sure but generally is regarded to be the result of irregular slumping during or just after deposition of the sediments in a body of water, caused by the weight of overlying sediments. The last example I shall take up is Pothole Arch (fig. 18), which differs from all the other examples in that this arch is roughly horizontal rather than vertical. Most park visitors, including me, were not aware of this interesting feature until after publication of the pamphlet “The Guide to an Auto Tour of Arches National Park,” which, as previously noted, may be purchased at the Visitor Center. Pothole Arch caps a ridge high above the road half a mile northwest of Garden of Eden, so only those who happened to look up at the right place were aware of its existence. A different mode of origin than that given in the caption for figure 18 is depicted on a poster in the Visitor Center, which shows the pothole being formed by a waterfall having an apparent flow rate of several cubic feet per second. Potholes can be formed in this manner in places where sufficient streamflow is available, either continuously or following rainstorms, but I believe the process depicted in figure 18 is a more likely mode of origin for Pothole Arch. How to See the Park As aptly stated on a poster in the Visitor Center, how to see the park depends in part upon the question “How long can you stay?” Inasmuch as the park entrance and Visitor Center are beside a through U.S. Highway (163), many motorists first become aware of the park’s existence from the entrance sign, and some take time for at least a quick visit, such as a round trip to The Windows section, which can be made in an hour or so.