138 DIVISION OF TRAILS — EIVEE COURSE. 



proceeded ; a small exploring party continued the trail along the river bank, so as to examine 

 the caiions 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 2^ 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. 



