2Cz|. Sct)TT (>;/ ///e Birih of Arizona. [Apri! 



built. These are the principal forms of trees and shrubs charac- 

 teristic of the great plain of Tucson, but there are many others 

 too numerous to bring into consideration in the present papers. 



The region of the valley of the Gila River at Florence is very 

 similar to that about Tucson, though the mountains are lower 

 and more distant, vvdiile the plains back from the river valley 

 proper ai'e more broken, and generally a little higher in average 

 altitude. The road leading to Riverside from Florence passes 

 through this arid plain, and by a gradual ascent reaches the low 

 mountains west of the former place. The plant and tree forms 

 already described ai'e very characteristic of this entire route, and 

 are very abundant the wiiole wav, until reaching the summit of 

 these low mountains. Here the most conspicuous forms are sev- 

 eral kinds of yucca, and the aloe (yAgave ainericattd) or mescal 

 plant, all of which are common. After passing the summit the 

 road again descends into the valley of the Gila, passing through 

 a hilly region cut by many large arroyas, most of which during 

 the rainy season become running streams. The plants of these 

 low hills are chiefly the different forms of mesquite, but the giant 

 cactus is everywhere present. 



The valley of the Gila at Riverside is \'ery narrow, high hills 

 and mountains rising abruptly on either side. The Mescal 

 Mountains to the north of the river are really the higher foot- 

 hills of the Pinal Range, and the lower hills to the south are off- 

 shoots of the Santa Catalina Range. Along the river banks are 

 great groves of cottonwoods and sycamores, and back of these a 

 growth of mesquite and cat-claw, running almost immediately 

 into a mixed vegetation consisting of palo-verde, mesquite, giant 

 cacti, chollas, prickly pears, and ocotillas, the valley beginning to 

 break into low hills and mesas just a little back from the 

 river's edge. The altitude of Riversitle, as given by the govern- 

 ment survey, is about 3300 feet. 



The region at the headwaters of Mineral Creek has an alti- 

 tude approximating 5000 feet. It is some six miles to the east- 

 ward of the divide made bv the summit of the Pinal Mountains, 

 where collections were made. Here are some large isolated cot- 

 tonwoods, many sycamores, and on the small plains and mesas 

 varieties of cat-claw and ipesquite ; junipers of considerable size 

 form groves, and a variety of the hackberry tree is not uncom- 

 mon. The flow of water in Mineral Creek is even more desul- 



