Geology of Ft. Apache Region, Ariz. — Reagan. 267 
LITERATURE. 
Dr. Arch. R. Marvine passed through the region under con- 
sideration in 1 87 1 from the Little Colorado river to Fort 
Apache, then called Camp Apache; and from thence he went 
via the San Carlos river to the Gila valley. While on this trip 
he examined the rocks over which he crossed, obtaining sec- 
tions, and other valuable information. Dr. G. K. Gilbert also 
visited Camp Apache in 1873. While there he made three side 
trips ; the first to the White mountains or Sierra Blanco coun- 
try, the second up the North Fork of White Mountain river, 
and the third to the junction of the main forks of the river. 
These men both belonged to the U. S. Geographical Survey 
corps. Their respective reports may be found in Volume III. 
of the U. S. Geographical Surveys west of the 100th Merid- 
ian. A further discussion of the above citations will be given 
when the respective areas concerned are considered. 
GENERAL DESCRIPTION. 
The Fort Apache region is in east central Arizona between 
longitude 109 degrees 30' and in degrees 10' W; between 
latitude 33 degrees and 34 degrees 20' N. Roughly speaking, 
it is a trapezium in form, its longest line being at the south- 
west, its shortest on the east. Its margin on the north is 
formed by the Alogollon range, on the east by the White moun- 
tains, on the southeast by Black river and the Nantanes and 
Apache mountains, and on the southwest by the Pinal and 
Sierra Ancha mountains and the Tonto basin. It is in the 
southwestern part of the great Rocky Mountain Plateau dis- 
trict, the fault along the western side of the Apache mountains 
being the southwestern limit of that plateau. 
The region, which is practically impassable except by trail, 
presents a diversity of appearance. It is a great basin whose 
rim is the mountains mentioned above. This rim is for the 
most part from 7000 to 11000 above sea-level, while the centre 
of the area at the west is only 3000 feet in altitude. Through 
its centre from the southeast, with a bold curve to the west, 
passes Salt river, whose tributaries drain the various slopes. 
To return to the rim, the Mogollon range is an elevated grassy 
plain, on which are fine forests of pine and fir. The White 
mountains are a volcanic area from which lavas have flowed 
