. Bulletin. Agriculture. 12 DROUGHT RESISTANCE OF OLIVE IN SOUTHWESTERN I ' 1 nil Fig. 2.âDiagram showing the mean monthly rainfall at Casa Grande, Maricopa, Phoenix, and Mesa, Ariz., as presented in Table I. The country around Casa Grande is a wide plain, through the level of which the mountains appear to be thrust up, so abruptly do the scattering groups and single low peaks break the surface. These mountains are largely composed of a soft, rapidly dis- integrating granite, with much feldspar in its composition, and their decay determines the char- acter of the soil, which is coarse
. Bulletin. Agriculture. 12 DROUGHT RESISTANCE OF OLIVE IN SOUTHWESTERN I ' 1 nil Fig. 2.âDiagram showing the mean monthly rainfall at Casa Grande, Maricopa, Phoenix, and Mesa, Ariz., as presented in Table I. The country around Casa Grande is a wide plain, through the level of which the mountains appear to be thrust up, so abruptly do the scattering groups and single low peaks break the surface. These mountains are largely composed of a soft, rapidly dis- integrating granite, with much feldspar in its composition, and their decay determines the char- acter of the soil, which is coarse and gravelly around the moun- tain base, sandy with more of clay a little farther awa}^, and of a stiff clay nature mingled with bars of sand and gravel along the drainage courses, scarcely as 3^et marked as stream channels, which serve to carry away the run-off from the occa- sional torrential rains so char- acteristic of the region. The most important of these water courses, sometimes digni- fied on the maps by being called the Santa Cruz River, is locally given the more appropriate name "Santa Cruz ; While along its upper course, from the Mexican boundary down to Tucson, there is a pretty well-marked channel and a more or less continuous flow of water, in the neighborhood of Casa Grande a slightly cut channel, a broad, well- marked flood area, and a still broader belt of mesquite growth mark the course of the so-called river. The popular idea that there is a strong underflow of water the entire length of this valley is given support by the heavy belt of mesquite which occurs with more or less regularity along the course. This tree is well known through- out the desert regions of the South- west as possessing a remarkable root system, able to penetrate to water- bearing strata at depths of 30 to 50 feet. The further fact that the railroad wells along the line of the Southern Pacific Company, particularly those at ]\Iaricopa and Casa Grande, 2 or 3 miles away
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