48 



verj^ mouth of the Colorado River. His observations are 

 briefly recorded on pages 21, 22, 125-132, and elsewhere, in 

 his monograph on ''Mammals of the Mexican Boundary of 

 the United States" (1907). Unfortunately no detailed publi- 

 cations have yet appeared concerning the results of the 

 Biological Survey field work. The botanical studies of the 

 Desert Laboratory parties, as well as the history of earlier 

 investigation from the days of the Spanish explorers, have 

 been summarized in MacDougal's important book ''The 

 Salton Sea" (1914), with citations of the principal published 

 sources of information. 



In February, 1905, Mr. Samuel N. Rhoads, of the Phila- 

 delphia Academy of Natural Sciences, made a boat trip from 

 Yuma to the mouth of the Hardy River, his collections and 

 notes subsequently forming the basis of a report on the birds 

 and mammals of the delta (Stone and Rhoads, 1905). Side- 

 lights on the general character of the country, its chmate 

 and fauna, have moreover been cast by numerous popular 

 articles by American sportsmen in Outing, Recreation, Field 

 and Stream, and similar non-technical periodicals. 



Although not applying specifically to the Mexican portion 

 of the Colorado Desert, a list by Van Rossem (1911) of winter 

 birds of the Salton Sea, and more particularly an admirable 

 treatise by Grinnell (1914) on the mammals and birds of the 

 lower Colorado Valley, are of utmost importance to those 

 interested in the zoology of the area. 



Zonal, Faunal, and Associational Status of the Region. 



Grinnell (1914) has confirmed the supposition that the 

 country contiguous to the lower Colorado River should be 

 assigned entirely to the Lower Sonoran Zone, and to the 

 fauna designated as the Colorado Desert. The same limits 

 undoubtedly apply to the section of northeastern Lower 

 California described herein, although at the southern extremity 

 of the region, west of the head of the Gulf of California, the 

 relatively narrow riparian belt is bounded abruptly by high- 

 lands that rise to the Boreal Zone in the mountains of San 

 Pedro Martir. 



