DAVIS: THE GRAND CANYON OF THE COLORADO. 143 



esplanade as dependent on structure, as will be considered further 

 on, the break in its floor would occur at the fault line whether the fault 

 was earlier or later than the erosion of the canyon. The small reces- 

 sion of the Red-wall cliffs in the Toroweap valley near Vulcan's throne 

 (c, p. 94) is explainable by their relatively recent exposure in the 

 canyon cycle, by the failure of erosion as yet to disclose any weak un- 

 derlying beds, and by the protection of the base of the cliffs by lava 

 floods, as will be more fully described further on in the section on the 

 Toroweap. The location of this valley in close association with the 

 fault line suggests that the fault originated before the valley was 

 begun, that is, before the initiation of the canyon cycle ; and this view 

 is borne out by the strong recession of the Triassic (Vermilion) and 

 Shinarump cliffs on the eastern side of what appears to be the same 

 fault line in the neighborhood of Pipe spring. As my interpretation of 

 the stratigraphy here differs somewhat from Button's, the case must be 

 presented in detail. 



The Sevier Fault Southwest of Pipe Spring. — The great Sevier fault 

 is described and mapped by Dutton as coming southward from the High 

 plateaus and ending near Pipe spring (c, p. 20), while the Toroweap 

 fault is said to end northward at the head of the valley of the same 

 name, twenty miles from the canyon (c, pp. 20, 93). A longer exten- 

 sion of the Toroweap fault is indicated by Powell, who briefly stated 

 that where it " crosses the Vermilion cliffs " its throw " is only about 

 two hundred feet ; " but he does not specify that the crossing is at Pipe 

 spring (a, p. 186). It happened that on our excursion we had good 

 opportunity of seeing the general features of the Pipe spring district, 

 where we noted that the cliffs formed on the Triassic and Shinarump 

 sandstones were distinctly displaced with respect to what may be called 

 the Sevier-Toroweap fault line. Hence, instead of curving the Sevier 

 fault to the southeast and ending it near Pipe spring, as it is drawn on 

 Dutton's map, it seems better to continue it to the south-southwest till 

 it joins the known Toroweap fault. Where the fault-line thus ex- 

 tended crosses Antelope valley, a shallow depression in the broad 

 plateau surface south of the Shinarump cliffs, its occurrence is not so 

 easily proved as in the neighborhood of the cliffs. As indicated in 

 Figure 11, both the Triassic and the Shinarump cliff-makers stand 

 about ten miles further north on the heaved (eastern) than on the 

 thrown (western) side of the fault near Pipe spring, thus indicating not 

 only an important dislocation, but a relatively long time since its pro- 

 duction. This is the rule of the region. Similar large measures of 



