JOHNSON: GRAND CANON DISTRICT. 153 
ent decrease due to the location of the lava flows, as suggested by 
Davis ('03, p. 20). 
Near the head of the Toroweap Valley the beds on the western side 
of the valley flex downward toward the east, while lower beds on the 
eastern side of the valley dip in the same direction. The presence of 
the Toroweap Fault is thus indicated, as well as the fact that the beds 
of the downthrow flex downward and the beds of the ui)throw flex 
upward as the fault plane is ap]>roached, a peculiarity noted repeatedly 
in the faults of this region. The monoclinal folding which preceded 
the faulting and determined the direction of the flexing noted, was 
presumably older than, and distinct from, the westward-facing 
monocline farther northeast, which is a part of the later fault displace- 
ment. 
At two places along its course the fold or fault disappears under 
volcanoes which are built over the zone of displacement, part of the 
cone being on the upper and part on the lower side. One is a short 
distance west of Sawyer's Tank, the other near the head of the Toro- 
weap Valley. In neither case does there appear to be any doubt that 
the displacement visible on either side of the volcanic covering is the 
same and continuous. 
The Toroweap Valley was regarded by Dutton as one of the ancient 
tributaries to the Colorado whose valleys were carved before the faults 
developed (Dutton, '82, pp. 94, 99, 201). This interpretation was 
based in part upon general considerations already referred to and in 
part upon the fact that the Esplanade (upon which the Toroweap 
Valley opens and with reference to which level the valley was believed 
to have been developed) is displaced where the Toroweap Fault 
crosses it. That the break in the level of the Esplanade does not 
afford evidence of a recent date for the fault has been pointed out by 
Davis ('01, pp. 143, 174). In addition to the fact that the valley 
closely follows the line of displacement, there are two features which 
indicate an ancient date for the fault. 
As in the case of the Sevier Fault, the drainage in the Toroweap area 
is in part across the displacement, from the downthrown to the up- 
thrown side. Sawyer's Tank is formed by building a dam across a 
narrow gorge in the monocline, to intercept the drainage, which flows 
from the low area eroded on the soft rocks of the downthrow side, 
through the monoclinal uplift, to the upthrown area east of the fold. 
That the Toroweap Fault is not a recent development is further 
