DELTA AND DESERT VEGETATION. 



Daniel Trembly MacDougal. 

 (with SEVEN figures) 



The systematized discussion of the deserts of North America 

 recently attempted by Mr. Coville and the author 1 made it obvious 

 that the southern extension of the Nevadan-Sonoran desert in Sonora 

 and peninsular California around the head of the Gulf was practically 

 a terra incognita to the naturalist. 



The waters of the Gulf have been surveyed and the more promi- 

 nent features of the shore lines traced, but since this work was done 

 thirty years ago, the charts, originally made from data collected by 

 "Commander" George Dewey in 1873-75, are sadly in need of 

 revision, especially in the region contiguous to the mouth of the 

 Rio Colorado. The positions of the prominent hills and mountains 

 visible from the sea have been plotted as range marks for the navi- 

 gator, but the maps bearing the results are difficult of interpretation 

 by the explorer on land. 



A fair share of attention has been paid to the animal life of the 

 river and Gulf, but the extensive areas around the mouth of the 

 river and the head of the Gulf have so far practically escaped investi- 

 gation. These regions offer difficult problems of transportation and 

 subsistence to the explorer. The southern part of the delta inclu 6-e 

 vast areas of muddy salt flats cut by a labyrinth of shallow pools and 

 channels, and joining directly the desert slopes and plains of Baja 

 California and Sonora. The water in the lower course of the river 

 is brackish for a distance of 3o km from the sea, while other sources of 

 water are uncertain and widely separated, the tropical sun forming 

 an additional factor to test the endurance of the unaccustomed 

 traveler. In running the boundary on the long northwestward slant 

 of the Arizona-Sonoran line after the Gadsden Purchase Treaty, 

 the commission found it necessary to haul water nearly 200 km to 

 meet the needs of its camps. The trail which runs near the bound- 



1 Coville, F. V. and MacDougal, D. T., The Desert Botanical Laboratory of 

 the Carnegie Institution. November, 1903. Washington, D. C. 



44 [JULY 



