MOVEMENTS OF VEGETATION IN THE SALTON SINK. 119 



the Colorado River. The main current of the Colorado no longer followed the channel 

 which had carried the main flow for a long period and now made a more southwesterly 

 course down the Bee River, which brought its waters directly against the southern end of 

 the Cocopah Mountains. It appears, therefore, that water was poured into this basin in 

 such manner that the lake was maintained continuously from 1910 until late in 1912, at 

 which time this manuscript was prepared. 



The maximum-level strand was marked by a heavy band of Prosopis, where it cut 

 across bajadas or detrital slopes, and by a distinct water-line along the rocky mountain 

 wall of the Cocopahs. The high beach of 1905 was marked by a zone of Sesuvium sessile and 

 by the remains of other halophytes, which had perished with the desiccation of the salty 

 soil. This preliminary visit showed the importance of carrying on observations in this basin 

 concomitantly with those to be made in the Salton Sink, but the internal disturbances of 

 Mexico were followed by military operations at Calexico and along the northern margin of 

 the Pattie Basin, which made field work impossible south of the international boundary. 



PLAN OF FIELD WORK IN THE SALTON SINK. 



An ideally perfect method of investigation would have been to make frequent exami- 

 nations of the entire shore-line of the lake, but as this was over 150 miles in length and 

 as parts of it lay below deserts accessible with difficulty and was fringed with mud flats, 

 this was practically impossible. Attention was therefore devoted to areas, a mile or loss 

 in width, back from the shore, which extended down the slopes with the recession of the 

 water. One such area was located at the extreme northwestern end of the lake near 

 Mecca. The soil consisted of a clayey alluvium, uneven as to saline content and detail 

 of surface, but in general showing a slope in which the fall was about 1 in 400, giving many 

 effects of a flat surface. The moister places maintained Typha, Populus, Salix, and Phrag- 

 mites; the saline spots bore such halophytes as Atriplex, Succda, and Spirostachys, while 

 mats of Distichlis were found scattered over the area. 



A second area was selected on the shore to the south westward of Imperial Junction, 

 on a clayey slope in which the adobe soil was high in salt content and bore scattering plants 

 of Atriplex, Suceda, and Spirostachys. The slope here was slightly steeper than the one at 

 Mecca, the fall being about 1 in 300. 



The steep detrital slope running down from the mountains to the southward of Traver- 

 tine Rock on the southwestern side of the lake bore a xerophytic vegetation, among which 

 were a few halophytes, such as Atriplex; the remainder were chiefly spinose and sclero- 

 phyllous forms. Bands or rows of these plants indicated ancient strands, some as high as 

 the maximum level of the ancient lake. (See Plate 18.) The slope here was about 1 in 

 20. On account of these old terracing effects, which were duplicated by the present lake, 

 tills place was designated "The Travertine Terraces." 



The shore-line of Obsidian Island, which lies to the westward from the Imperial Junc- 

 tion beach, about 8 miles from the recent high-water level, was examined over its entire 

 length of sand and gravel strands and rocky shores. The upper parts of the island bore 

 four species of Atriplex, some Spirostachys, and one or two other halophytes. In places the 

 beaches showed a fall of 1 in 7 or 8. 



A few examinations were made at various places on the western shores of the lake, 

 which lay across the lower parts of long bajadas or detrital slopes coming down from 

 the distant mountains. Some sand dunes were present on these slopes and the vegetation 

 included a variety of halophytes and sclerophylls. 



Sterilized islands, in the form of hill-tops emerging from the receding water, came in 

 for very detailed attention. The surface of Cormorant Island, north of Obsidian Island, 

 was not submerged, but was sterilized by the salty water at the high level. Various smaller 



