20 
THE GEAND CAlJON DISTEIOT. 
the highest importance, since it is the boundary, not only of the Grand 
Canon district, but of the Plateau Province itself. It drops the country on 
the west about 6,000 feet at a maximum. The greatest observed displace- 
ment is at the lower end of the Grand Canon, where the lower Ti’ias appears 
abutting against the lower Carboniferous. South of the river it continues 
for an unknown distance, still terminating the platform of the district. North 
of the river it diminishes in the amount of displacement, and near Saint 
George, on the Utah boundary-line, it appears to vanish. But the down- 
throw has in the mean time been shifted eastward to the Hurricane fault. 
As the Grand Wash fault diminishes northwardly so does the Hurricane 
fault increase. 
The latter crosses the Colorado upon the western base of the Uinkaret 
Plateau, and is known to extend a considerable distance south of the river; 
but the more distant extensions of it in that dii’ection have not yet been 
studied. At the Grand Canon its displacement is about 1,800 feet, and 
this amount is preserved with approximate uniformity for thirty miles north 
of the river. It then increases until, at the point where the Virgen River 
crosses it, the displacement is more than 6,000 feet, bringing the Jurassic 
below the level of the upper Carboniferous. Here by the evanishment 
of the Grand Wash fault it has become the boundary of the Plateau country. 
It continues northward in great force along the base of the Markagunt 
mass and disappears seventy or eighty miles north of the Virgen. 
The next fault is the Toroweap. It is of less magnitude and length 
than the others, though still considerable. It crosses the Colorado at the 
foot of the Toroweap Valley, which lies at the eastern base of the Uinkaret 
Plateau. Here its displacement is about 7U0 feet. It is seen to extend 
south of the river for a considerable distance, rather increasing in the 
amount of shear, or at least holding its own as far as it has been traced. 
But its mode of resolution remains to be investigated. North of the river 
it gradually dwindles and vanishes about 18 or 20 miles north of the Canon. 
The southern extension of the great Sevier fault also penetrates the 
district, but its effect is seen only in the terraces. It is a strong feature at 
the southernmost promontory of the Vermilion Cliffs at Pipe Spring, but 
its further extension towards the south cannot be great. The soil and allu- 
