138 
DIVISION OF TRAILS—RIVER COURSE. 
proceeded ; a small exploring party continued the trail along the river hank, so as to examine 
the canons of the Gila and the San Pedro river. The geology of this latter route alone is 
described. 
Along the river above, where the trails diverge, low granitoid ranges approach the river and 
narrow its bottom. These ranges occur on both banks of the stream, which, in some places, is 
not more than 30 feet wide and deep, having its banks thickly planted with cotton-wood, 
willows, cane, and mesquite. The river water is clear and good, and the bottom a micaceous 
granitic detritus. 
Plate IX, fig. 1, displays a geological section from Big Horn mountains to the basalt mesa. 
Plate X, fig. 1, illustrates the geology from the Pimas villages to the Gila river; fig. 2, the 
structure of the hill at camp July 6, referred to on the next page ; and fig. 3, a section along 
the river to illustrate its notice in the next chapter, where it is described on page 140. 
