CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 289 



The low plains are dominated by Larrea-Franseria, with various 

 associates, as in the Mojave Desert. Because drainage here is not 

 internal, margins of streambeds support a distinctive mixed com- 



FlG. 154. Mesquite (Prosopis chilensis), a common ground-water indica- 

 tor in the desert scrub formation —Courtesy Univ. of Nevada Agricultural 

 Extension Service. 



munity including species of Prosopis, Cercidium, Olneya, Dalea, 

 etc. In the higher elevations of Arizona and northern Sonora 

 (1,000-2,000 feet), there is a great mixture of species and life 

 forms. Although numerous species characteristic of the other des- 

 erts are present, Cercidium microphyllum is a dominant with num- 

 erous arborescent and columnar cacti, including Carnegiea giga?i- 

 tea, Lemaireocereus schottii, and many species of Opuntia. The 

 variable topography of the peninsula of Lower California supports 

 an equally variable flora including many species. Near the coast, 

 there are more leaf succulents than in any of the other desert 

 areas. 



Chihuahua Desert— Extending from southern New Mexico 

 southeastward to western Texas and down into Mexico, much of 

 this area is interrupted by high mountains and lies between 4,000 



