Geology of Ft. Apache Region, Ariz. — Reagan. 287 
has captured all the eastern drainage and become the master 
stream. 
The Sierra Ancha. — The Sierra Ancha extends from Salt 
river in a northwestern direction some twenty or thirty miles, 
as a massive, faulted block, with its steepest slope on the north- 
east. This block is composed of Tonto sandstone at the crest, 
beneath which are Algonkian and Archaean rocks. 
The Mogollon Range or Mesa. — This mesa extends from 
the vicinity of Fort Apache in a northwestern direction, and 
is of an average width of ten to fifteen miles, and an altitude 
ranging from 6000 to 7500 feet. The Carboniferous strata pre- 
dominate, but the eastern and southern extensions are covered 
by basaltic eruptions. This mesa contains the greater part of 
the pine and fir timber belt of Arizona. It is also a grazing 
region. Mr. Oscar Loew visited this region in 1873 an d in his 
report he notes the following facts : 
"This timber-covered plateau extends from the vicinity of Camp 
Apache in a northwesterly direction to the vicinity of the southern 
extension of the San Francisco mountains, and is of an average width 
of ten to fifteen miles and an altitude of 7000 feet. It was the source 
of former grand rivers as is testified by canyons of gigantic dimensions. 
The canyon of Big Dry fork, for instance, is over seventy miles in 
length and from two hundred to four hundred feet in depth; the walls 
are principally sandstone, with here and there limestone, and descend 
in terraces : sometimes, however, are quite vertical. Around the small 
ponds or little rills on the bottom of this remarkable canyon an ex- 
traordinary vegetable life has been developed. Nothing of the canyon 
is noticed until one stands on the very margin, where a pathway to 
the other side is looked for in vain. It was a tributary of the Colorado 
Chiquito. Its head at the present time is formed by a small creek 
that sinks when it reaches the juniper region. Numerous creeks head 
in this plateau. Among them are Chevelon's fork. Cedar creek, and 
Carrixo creek. The Tonton basin, a deep depression, borders this 
plateau on the south side. The Carboniferous strata predominate, hut 
the southern i and eastern] extension is covered with basaltic eruptions. 
Here are many forests, meadows and fine valleys suitable for farming 
and stock raising.' 55 
This mountain is the result of a faulting and tilting on a 
grand scale. The faulting took place along the line of the 
Kelley-Salt river dike. The dip of the block north of the 
fault is constant and in a northern direction ; but the dip of the 
blocks on the south is variable, some dipping towards the dike, 
others from it. And today East fork of White river. White 
