13 CiEOLOGY. 



is frequent in the valleys, and everything indicates a capacity for cultivation, the grazing capa- 

 bilities being unequalled by any tract heretofore passed over. 



Beyond this the San Pedro valley spreads out in diverging branches to the east and west, thus 

 drawing tributary a very extended mountain drainage. 



It is this latter character which sufficiently accounts for the fact that the San Pedro is the 

 only branch of the Gila Kiver, coming from the south, which furnishes an uninterrupted stream 

 of running water along its whole course. 



At the point where the main valley of the San Pedro is reached we find an alluvial belt, 

 variable in width, and occasionally marshy. These bottoms are flanked by terraced table-land 

 of unequal heights, composed of a hard gravelly soil, and supporting a close sward of grama 

 grasSj giving a peculiarly smooth shorn look to the general face of the country. 



Occasional exposures of igneous rock, or the projecting spur of some mountain ridge, serve to 

 diversify the scene ; and quite constantly in the higher branch valleys is exposed a form of 

 igneous conglomerate. This latter formation is exposed in irregular bluffs along the edges of 

 these valleys, presenting washed faces and precipitous walls crowned with terraces. These 

 higher points are frequently set ofl" with the remains of deserted dwellings, plainly located 

 ■with a view to defence. Other eminences, commanding extensive views, are occupied by rocky 

 breastworks, serving the double purpose of watch-towers and strongholds of retreat. Associated 

 with these are also extensive rocky enclosures, in which the cattle were secured. All these 

 points are suggestive of the condition of constant warfare to which this commencing civiliza- 

 tion was subject, and under which it was at last obliged to succumb. 



These upland valleys are only sparsely wooded by occasional cotton-wood or walnut trees. 

 As we approach the mountains, however, the timber growth becomes more abundant, and the 

 lower ridges are occupied by extensive groves of oak, which, on the higher points, are associated 

 with pine and cedar. 



From the head of the " Nutria" (southwest) branch of the San Pedro, up which our road 

 passes, we commence the steep ascent of the mountain ridge lying between the Santa Cruz and 

 San Pedro valleys. The character of this range is exactly similar to what we have before de- 

 scribed as pertaining to all the higher mountains passed over on our route, west of the Sierra 

 Mad re. 



The height of the pass leading to Santa Cruz is not less than 1,000 feet above the respective 

 valleys on either side, being equally steep and rugged on either slope. The same ridge, ex- 

 tending toward the south and southwest, forms a continuous line of high mountains, lying 

 between the San Pedro and Santa Cruz valleys ; the preferable route for crossing is probably 

 that taken by Col. Cooke in 1846. 



The upper route, being the one more commonly followed, strikes the Santa Cruz valley near 

 its head source. 



The direction of this valley is at first nearly due south, giving the idea that its drainage is 

 on the line of the rivers flowing south to the California Gulf. It is indeed so laid down on 

 most of the maps of this region, but this is manifestly incorrect. About three miles south 

 of the town of Santa Cruz the valley makes a sharp elbow ; thence doubling on its former 

 course, it continues north and northwest, being the same valley in which, lower down, are 



