168 THE SALTON SEA. 



soonest perish on account of the increasing aridity. The final condition of this beach would 

 probably be one in which Isocoma would endure, although no estimate of the behavior of 

 the other species can be made except to point out that they are not on the slope just above 

 the high level of the lake, which is of the extreme desert type of this region. 



The two beaches which have thus been analyzed display different types of behavior. 

 The gently sloping alkaline Imperial Junction beach received a sowing of 17 species during 

 the first year of emersion and no secondary introductions. The stress of increasing aridity 

 has depleted the number of the pioneers until but 5 species remain, of which one, Pluchea, 

 will soon fail for lack of sufficient soil-moisture. The final flora of the slope will probably 

 consist of species now occupying it, but with greatly reduced number. An occasional indi- 

 vidual of one or two other species may come in. 



The Travertine Terrace of 1907 was probably subject to wave action during the greater 

 part of that year and its original occupants may be taken to include 13 coming on in 1908; 

 these were quickly reduced to 4 species two years later, when secondary introductions 

 began, of which Pluchea sericea and Isocoma have played an important part. The last 

 named may be regarded as a plant which would be suitable for endurance of the final condi- 

 tions of the desiccated slopes of this locality. 



ANCIENT STRANDS. 



The strands of the Travertine Terraces were on the crest of an arched slope or bajada, 

 which would ultimately be subjected to the maximum action of the wind, which is the 

 more important meteoric feature in this region. In consequence of its action it was not 

 possible to find the ancient beach ridges or the edges of terraces which would correspond 

 in position to the vertical banks which marked the mid-winter level of the Salton during 

 the recent period of the lake. But a number of well-marked strands were to be recognized, 

 lying at various levels within 100 feet of the level of the ancient high beach-line. These 

 beaches owe their preservation to the fact that they were formed on the concave part of 

 the slope and in places sheltered from the prevailing wind and with no run-off. These 

 were well marked to the southward of Travertine Rock and also to the westward. The 

 character of these strands is such that they may not be safely taken for seasonally formed 

 strands, but each one might be considered as marking the maximum level of the lake at 

 some previous filling. This assumption is supported by the fact that such well-marked 

 beach ridges were not found anywhere near the present level of the lake (see Plate 29 b). 



Ancient strands of well-marked structure are to be seen on the steep slopes westward 

 of Salton Slough, where a hill rises to such a height that its summit was covered at the 

 highest level of Blake Sea; 83 well-marked beach ridges were seen on the slopes of this hill 



in 1910. 



An examination of a strand south of Travertine Rock was made m October 1912, and 

 a photograph was taken (see Plate 30 a). The plants marking its position was a compara- 

 tively dense desert formation inclusive of Atriplex canescens, Coldenia palmeria, Fransena 

 dumosa, Hymenochloa salsola, Parosela emoryi, and Petalonyx thurberi, all of which were 

 restricted to a band or zone which varied from 12 to 18 feet in width. A second examination 

 of another strand in February 1913 included the above except Atriplex canescens. 



It is notable that Parosela and Atriplex, which are members of this formation, which 

 dates the beginning of its development back for at least a century or two, also appear on 

 similar strands on Obsidian Island and elsewhere shortly after emersion. 



THE REOCCUPATION OF STERILIZED ISLANDS. 

 The slopes of the Sink were interrupted at various places by small elevations consisting 

 of rock in place, the most notable elevation being in the southeastern part of the submerged 

 area. Three of these hills rose above the highest recent level of the water, and detailed 



