128 PLANT WORLD. 



garlic, and the mountains, peaks, and valley which bear this 

 name, were so designated because of the abundance of the 

 plant in their vicinity. When our Mexican guide pointed out 

 the so-called garlic, however, it proved to be Hesperocaliis 

 ituditlaliis, a liliaceous plant with a bulb eight to sixteen inches 

 below the surface, from which the flower stalk and the 

 crinkled leaves are sent up during February and March. The 

 plant is found from northern Arizona to far south in Sonora. 

 The general structure of the oasis of Sonoyta is fairly 

 representative of such formations in American deserts, and 

 its principal features merit description. A great ovoid plain 

 forty or fifty miles across, lies mostly south of the inter- 

 national boundary with Its narrower and lower portion to 

 the westward. The plain, once a great basin-like valley, is 

 now filled with detritus from the encircling mountains to a 

 depth of a few hundred feet. The greater part of the precip- 

 itation here and on the slopes of tlie neighboring mountains, 

 sinks down in this broken material, forming running streams 

 on the surface only during seasons of great precipitation. 

 The water percolating through the detrital mass gradually 

 makes its way toward the lowest part of the original valley, 

 this being facilitated perhaps by layers of clayey material or 

 harci-pan impervious to water, with the result that in follo\\- 

 ing this horizontal layer it is brought to the surface by 

 various converging lines of drainage at the lowest part <>{ 

 the gravel-filled xalley, this occurring within a mile of the 

 international boundary in the present instance. The stream 

 formed, flows along over the margin of the clayey layer, being 

 exposed to enormous evaporation, and furnishing a supply 

 which may be led out in conduits for irrigation purposes. 

 Lower down it encounters the sand or gravel beneath the 

 clay and again it sinks into the ground. In the brief 

 seasons of flood, the stream may run far down before it is 

 swallowed by the porous sands, and as aridity increases, the 

 end of the water recedes far up stream. It is this short reach 

 of living stream that forms the heart of the oasis, nourish- 



