ECHO CLIFF MONOCLINE. 
205 
It seems proper also to describe briefly the Echo Cliff monocline, since 
it is one of the most important in that great series of displacements which 
traverses the district from south to north. Everywhere it is a true mono- 
cline. It is known to extend more than a hundred miles south of the Colo- 
rado, and certainly reaches fifty miles north of the river. Upon the flank 
of the flexure the Permian Trias and Jura are upturned, forming lofty cliffs 
of very irregular aspect. Back of these the Cretaceous conies in as a series 
of steps. The irregular character of the cliff’s is due to the considerable 
inclination of the strata, causing them to weather into sharp towers and 
needles of very irregular form, instead of the systematic and regular pro- 
files which are generated where these beds are horizontal. The total down- 
throw of the monocline varies greatly from place to place, but along those 
portions where it has been well observed the total displacement ranges from 
3,500 to 4,000 feet. Its age is Tertiary, and probably very nearly coeval 
with the East Kaibab monocline ; in other words, rather late Tertiary. 
The proof of Tertiary age is conclusive, since the flexure bends the Creta- 
ceous beds wherever it approaches them and its northward continuation in- 
volves the Eocene. 
