220 GUIDEBOOK OF THE WESTERN UNITED STATES 
lower part of its course is through a thicket of mesquite. The route 
continues southwestward on an upgrade of about 200 feet to a pass 
through the Gila Bend Mountains, thus avoiding the big bend of the 
Gila River. On this grade there are fine views to the northwest 
showing very prominent buttes, peaks, and ridges of volcanic rocks 
rising steeply from wide desert valleys. The most conspicuous of 
these is Saddle Mountain, more than 2,000 feet high, which takes its 
name from a deep saddle-shaped depression in its top. These features 
mark a center of great volcanic activity in Tertiary time, with the 
outpouring of thick sheets of lava and a large amount of ash and tuff. 
The sheets of these materials have been gently tilted and flexed and 
considerably faulted, and erosion has cut wide valleys that isolate 
the ridges. In Saddle Mountain the beds are broken by many faults. 
sw. NE. 
Gila Bend Mts. 
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Ficure 59.—Section across the valley of the Gila River at Gillespie Dam, Ariz. After C. P. Ross. 
Ql, Quaternary lava; Tl, Tertiary lava; Ts, Tertiary sandstone; Agr, granite 
The rocks underlying this region are granite and schist of pre-Cam- 
brian age which present a rolling surface under the volcanic deposits. 
West of Crag the railroad reaches outcrops of lavas and other 
volcanic rocks which are extensively displayed in the pass at the 
divide near Harqua and in many surrounding ridges. 
In this desolate region the desert flora is well represented by various 
cacti, including scattered sahuaros, many covilleas, and much palo- 
verde and mesquite, the last named being most conspicuous along the 
dry washes. The volcanic succession has great thickness in the prom- 
inent flat-topped Woolsey Peak,” which is conspicuous to the south at 
intervals from Crag to Gillespie. Cimmerian Peak is the highest point 
58 According to C. P. Ross the rocks | which lie just east of Saddle Mountain, 
in Saddle Mountain consist of fine- | consist mostly of the younger basalt, 
of fragmental rocks, mostly volcanic | pioneer settler on the Gila River who 
agglomerates and breccias. Some of | engineered the ‘Pinole treaty,” in 
the rounded forms and hollows appear | which many Indians, invited to come 
to be due to a disposition to curved | unarmed to a feast and council, were 
_ exfoliation and not the result of solu- | treacherously set upon and slaughtered 
_ tion or erosion. The Palo Verde Hills, | by their host and his friends. 
