61 



zoologic phases, throughout a region where a low, intricate, 

 subtropical delta, an arid and abrupt mountain range, and a 

 barren, alkaline desert basin are in contiguity. 



I should like to apply, in so far as possible, the principles 

 of Grinnell's system to the present hasty reconnaissance of 

 the Mexican portion of the Colorado Desert. Since I have 

 little of a specific nature to report concerning the first five 

 (River to Quail-brush) associational groups in the list, these 

 may here all be combined under the broader ecologic heading 

 of ''Delta Area." The Mesquite Association, to be sure, 

 belongs in part to the delta, but it also extends in its pure 

 form (''orchard forest") over tracts many miles square, in 

 the southerly part of the Salton Basin, from the plain south 

 of the Alamo River almost to the northern point of the 

 Cocopahs; and, again, over much of the low land in Pattie 

 Basin. The Saltbush Association is in evidence in several 

 parts of Salton and Pattie Basins, notably at the southeastern 

 end of the latter, near the base of the Pinto Mountains. The 

 Creosote Association comprises large expanses around the 

 margins of both basins. As might be suspected, it is an 

 unimportant element on the western border of the delta fan, 

 below Volcano Lake and the Cerro Prieto. The Wash Asso- 

 ciation is especially well delimited^ extensive, and botanically 

 luxuriant on the rising land west of the Pattie Sink. It is 

 also more or less distinguishable at points along the eastern 

 side of the Cocopahs, and scantily elsewhere. 



I observed no giant cactus during our whole journey south 

 of the border, but there is a distinctive plant zone, very 

 likely corresponding to the Saguaro Association, along the 

 higher reaches of the stony incline below the eastern face of 

 the Tina j a Mountains and Peninsula Range. Here Fouquieria 

 splendens, in its most magnificent development, is far and 

 away the predominant floral feature. The area may perhaps 

 warrant the name "Ocotilla Association." Traces of it occur 

 also on the lower slopes of the Cocopahs and at the foot of 

 Black Butte. 



Brief notes upon the several associational groupings, and 

 their faunas, will be found in the following narrative and in 

 the list of birds. 



