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 Dutton’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 
