Vena 
DAVIS: THE PLATEAU PROVINCE OF UTAH AND ARIZONA. 25 
The view of south Toroweap valley from Vulcan’s throne is more 
extensive than that from the corner of the esplanade (Plate 5 A). It is 
partially shown in one of Holmes’s drawings (Dutton, b, Plate XVIIL). 
The further end of the valley turns gradually from south to southwest. 
The lower western wall curves out of sight and the higher eastern wall 
bends round so as to close the view ; hence the fault must turn westward 
with the valley. The lavas of the south Toroweap were poured out 
before the inner canyon had attained nearly its present depth, yet not 
until the valley had been eroded several hundred feet beneath the 
esplanade sandstone ; for the lava rests on a considerable thickness of 
ash (not distinctly shown in Holmes’s drawing reférred to above) exposed 
in the southern wall of the canyon, and yet the lava surface is at the 
west-esplanade level. The outburst of the lavas must have been long 
after the first and greater movement of the Toroweap fault, but the lava 
sheet is now broken by the recent smaller movement, apparently on or 
close to the old surface of fracture, as has already been stated. A short 
lateral gulch of the main canyon, apparently gnawed back along the 
new fault, divides the nearer part of the lava sheet into an eastern 
(higher) and a western (lower) portion. A small ash cone surmounts 
the latter ; it has been partly undermined by the widening of the gulch. 
The dikes that rise in the wall of the canyon, as if to feed this cone, 
figured in Dutton’s monograph (b, p. 96), confirm the date above 
suggested for these local eruptions with respect to the erosion of the 
inner canyon ; most of the depth of the canyon must have been eroded 
after the dikes were intruded. Two other ash cones are seen further 
south : one is about a mile from the canyon, close to the scarp by which 
the dislocation of the esplanade can be traced far along the valley ; the 
other is a mile or more beyond, on the lower Aubrey slope on the east 
side of the valley. Two small cones stand on the south esplanade, about 
a mile and a half east of the fault line. They are seen in Plate 4 B. 
They seem to be due to eruptions after the erosion of the canyon had 
nearly reached its present stage, for their lava flows into the head of a 
neighboring ravine whose length could not have been gained until the 
canyon was deeply incised. It seems remarkable that the ascent of 
lava to these cones should have so completely disregarded the oppor- 
tunity of finding a vent in the canyon wall. ‘There is no record that 
the south Toroweap has been visited by a geologist: all that is known 
of its structure depends on observations from the north side of the 
canyon, at distances of several miles. The southern end of the fault 
which guides the valley has not been closely determined, 
