THE PElJfCIPAL DISPLACEMENTS. 
19 
those of the plateaus. We may now realize that the district drained by 
the Grand and Marble Canons consists of a vast platform of Carboniferous 
strata nearly horizontal; bounded on the north and east by the edges of 
abruptly terminated Mesozoic beds ascending cliff above cliff; and bounded 
upon the west and south by its own terminal escarpment descending to the 
Silurian and Archjean rocks of the sierra region. 
In a preliminary treatment of the more general features of the district 
it is necessary to advert to the displacements which serve to define its dif- 
ferent portions. The most striking structural characteristic is the approxi- 
mate horizontality of the strata. But although tlie dips, except at the mono- 
clines are very small, they are important. They rarely exceed 2° and 
generally are less than 1°. But as they are for the most part in one direc- 
tion — ^towards the north — and as the distances over which they prevail are 
very great, the aggregate effect is correspondingly great. The summit of 
the Carboniferous at the base of the Permian near Kanab, five or six miles 
south of the Vermilion Cliffs, is about 4,400 feet above the sea. Forty 
miles further south, near the brink of the Grand Canon, the same geologi- 
cal horizon lies at an altitude of 6,400 feet, and at the bases of the San 
Francisco Mountains its altitude is 7,800 feet above the sea. In the course 
of the discussion this widely diffused dip will appear as a factor of the 
utmost importance. 
Allusion has already been made to the abrupt lines of displacement 
which traverse the region in directions which never deviate far from north 
and south. But some further discussion is advisable. 
The great faults and flexures which traverse lengthwise the district 
of the High Plateaus and the Grand Canon district form a very striking 
system. They are of great magnitude and are remarkable *for their enor- 
mous length. In the High Plateaus they are comparatively near together, 
but from north to south they spread out very slightly and the area over 
which they extend constantly widens southwardly. In the Grand Canon 
district they have their widest expansion and are separated by the widest 
intervals, occupying there a belt of country having a width of more than 
a hundred miles from west to east. 
The westernmost of these is the Grand Wash fault. It is a feature of 
