26 BOTANY. 
On the limestone rocks near Camp Bowie were Cevallia sinuata and 
Macrosiphonia brachysiphon, plants that we found to be by no means common. 
The Artemisias no longer formed the predominant feature of the plains 
landscape, as they had north of the Mogollon Mesa. 
The immense stretch of plain from Camp Grant south, gradually be- 
comes lower, until at Tucson it is but 2,400 feet above the sea. This plain 
as far as the San Pedro—say thirty-five miles north of Tucson (though, as 
before stated, in the main dry)—is covered with a luxuriant growth of gTASses 
of nutritious character, wherever, as at Sulphur Spring, moisture is found in 
sufficient quantity in the soil. The immediate slopes of the San Pedro 
Valley are densely covered with Atriplex, Sarcobatus, Sueda, ete., while 
the malarial cursed flats along the river produce heavy crops of the ordinary 
cereal grains and garden vegetables. Thence to Tucson the country be- 
comes more sandy, and even the Chenopodiacee give way largely to Larrea 
and various species of Cactacee. 
From Tucson south the plain again rises until at Tubac it is again at 
least 3,000 feet, and east of the Santa Rita Mountains Old Camp Crit- 
tenden stands at an elevation of 4,749 feet. Here we leave the area of the 
Colorado River drainage, and enter another, sloping toward Mexico. 
To generalize: we may say that from the Gila south almost to the 
Sonora line (along our route of travel), the country may be regarded as a 
plain with a gradual slope to the south, more or less barren and dry save 
along the river-banks, and in the immediate vicinity of springs; with the 
Pinaletio, Caliuro, Santa Catalina, and Chiricahua Ranges, and Dragoon 
and Santa Rita Mountains rising above the general level to a height of from 
6,000 to 10,400 feet, the middle altitudes or mesas shading off into plains 
below and leading to mountain elevations above, with in neither case a 
clear line of demarcation between. 
Indeed, we may go a step further and consider the entire country from 
South Park south to the Mexican line as a series of continental swells and 
depressions, illustrating still this southward slope. 
