According to Cater (1970, p. 65-67), who made an intensive study of the salt anticlines, collapse of their crests seemingly occurred in two stages—the first stage following Late Cretaceous folding; the second following uplift of the Plateau later in the Tertiary. Solution and removal of salt by ground water played the leading role in the ultimate collapse. [Illustration: TILTED BLOCK OF ROCKS IN CACHE VALLEY GRABEN, viewed to the east toward Cache Valley from point on gravelled side road to Wolfe’s cabin, about half a mile east of paved road. Steep slope on left composed of Jurassic Morrison Formation, hogback on top formed by Dakota Sandstone of Late Cretaceous age, and gentle slopes to right composed of the Mancos Shale of Late Cretaceous age. (Fig. 11)] As shown by Dane (1935, pl. 1, p. 121-126), collapse of the Salt Valley and Cache Valley anticlines was accompanied by considerable faulting and jointing, particularly along their northeast sides; by the upward intrusion of two large areas of the Paradox Member of the Hermosa Formation, one just northwest of the park and one in the middle of Salt Valley south of the campground; and by two downdropped masses of rock known to geologists as grabens (pronounced gräbǝns)—one just northwest of the park and one called the Cache Valley graben, which extends both east and west from Salt Wash. The Cache Valley graben has preserved from erosion the youngest rock formations in the park, as shown in figure 11. The remarkable jointing of the rocks on the northeast limb of the Salt Valley anticline is shown in figure 12. All the arches in this section of the park were eroded through thin fins of the Slick Rock Member of the Entrada Sandstone, and some, like Broken Arch, figure 16, are capped by the Moab Member.