DAVIS: THE PLATEAU PROVINCE OF UTAH AND ARIZONA. 19 
these beds make a much smaller part of the western wall. This evidence 
of a fault along the valley is abundantly confirmed at the canyon, where 
the dislocation in the southern wall is clearly seen in the grand view 
from Vulcan’s throne, as Dutton has told (b, p. 93). In my excursion of 
1900, our party had but a few hours at this point, and during much of 
that time I was so overcome with the heat that it was impossible for me 
to make any critical observations. During the past summer, much 
better opportunity for studying this most interesting locality was gained 
by camping over two nights, from July 21 to 23, on the esplanade just 
east of the fault line ; the only drawback on this occasion being that our 
stay there was during a period of haze brought by the southwest winds, 
and accompanied by sultry nights as well as excessively hot days. We 
carried water for our own needs from Oak spring, and watered our horses 
at a muddy reservoir made by the stockmen just north of Vulcan’s throne. 
The point on which I previously felt constrained to differ from the 
conclusions presented in Dutton’s report concerned the date of the 
Toroweap fault relative to the erosion of the canyon. It still seems 
necessary to regard the fault as for the most part of earlier origin than 
the canyon, because the valleys that follow the line of dislocation both 
north and south of the canyon are widely opened. Had the fault been 
produced after the erosion of the esplanade, that is, at so recent a date 
that even the vigorous Colorado has since then had time to carve only 
a narrow canyon, it would have been quite impossible for weak and 
intermittent wet-weather streams to have, in the same brief period, 
carved broadly open valleys, two or three miles wide, along the fault 
line. So late a date for the fault therefore makes it necessary to sup- 
pose that the broad north and south Toroweap valleys had been eroded 
during an earlier period, identical with that in which the esplanade was 
developed, and that the Toroweap fault line subsequently followed the 
course of the valleys: an extremely unlikely occurrence. It is much 
more probable that the greater movement of the fault antedated the 
erosion of the north and south Toroweap valleys, and that their location 
was in some way dependent on the fault. 
On the other hand, a relatively recent additional movement of a hun- 
dred or more feet is clearly indicated by the dislocation of a lava bed in 
the floor of the south Toroweap valley close to the canyon rim, as de- 
scribed by Dutton (b, p. 94). A corresponding movement is indicated on 
the north of the canyon in the gulch between the eastern base of Vulcan’s 
throne and the west-facing scarp of the esplanade, as in Figure 7. Near 
the base of the esplanade scarp there is a bench of firm black lava, which 
