LIFE ZONES 



the San Bernardino Mountains, 11,485 feet, is the highest moun- 

 tain south of the Sierra Nevada. San Bernardino, in the same 

 range, is 10,805. In Arizona, the San Francisco Mountains reach 

 an elevation of 12,794 feet. 



Six Life Zones are represented in the Southwestern United 

 States. 



Boreal Region : Arctic- Alpine, Hudsonian, and Canadian Zones. 

 Mostly above 8500 feet. Tops of high mountains. These Zones 

 are of comparatively small extent in our area and are not sharply 

 denned except on the San Francisco Mountains, where the forest 

 ceases at 12,000 feet. Barren mountain-tops above timber-line 

 represent the Arctic- Alpine. Hudsonian is marked by the limber 

 and fox-tail pines and the Clarke Nutcracker. The Canadian is 

 characterized by firs and lodgepole pine, the Williamson Sap- 

 sucker, Cassin Purple Finch, and Pacific Nighthawk. 



Transition Zone, 5500-8500 feet, is indicated by incense cedars 

 and yellow pine forests. Crested Jays, Nuthatches, and Chicka- 

 dees are characteristic birds. 



Upper Sonoran Zone, sea-level (coastal slope) to 5000 feet. 

 Sagebrush and chaparral, or elfin forest, of the foothills; Sage 

 Sparrow, California Jay, California Thrasher, and Anthony 

 Towhee are typical. 



Lower Sonoran Zone is that of the hot, dry desert below 3000 

 feet. Catclaw, mesquite, creosote, and giant cactus are typical. 

 The Cactus Wren, Crissal Thrasher, and Vermilion Flycatcher 

 are some of the characteristic species. 



In California valleys, and to a less extent in Arizona, much of 

 the original Lower Sonoran has been transformed to Upper 

 Sonoran through cultivation and irrigation. This has brought 

 corresponding changes in the bird life of such regions. 



Mount Wilson (Pasadena) rises to a height of 5886 feet. The 

 summit only is Transition. The rest of the mountain is all Upper 

 Sonoran. 



The great yellow pine forest plateau of Arizona bordering the 

 Grand Canyon is nearly all above 6200 feet (Transition Zone). 

 Above 8500-9000 feet this is replaced by firs, spruces, and aspen. 

 In southeastern Arizona, Transition Zone occurs as island areas 

 on high mountains, with a belt of Upper Sonoran, rising from a 

 Lower Sonoran plain. 



