TOPOaftAPHIC FEATURES OP THE DESEET BASINS. 4*7 



tTirning of the river toward the basin in 1905 and 1906, a condition 

 which it cost millions to remedy. Had no attempt been made to 

 return the river to its seaward bed, or had this attempt been unsuc- 

 cessful, the basin would have filled until it overflowed into the Gulf 

 or until the Colorado turned southward of its own accord. In either 

 case desertion by the river would have left an inclosed sea to slowly 

 evaporate as the Salton Sea is now doing. That this history was 

 actually enacted in the recent past is indicated by a deeply cut old 

 beach Hne surrounding the basin at about 40 feet above sea level and 

 a series of lesser and lower strands marking stages of retreat. The 

 similarity of conditions then and now is attested by the fact that this 

 older series of strands can not be distinguished from the strands 

 which have been formed by the retreat of the present Salton Sea. 



This interpretation of the recent history of the Salton Basin may 

 require modification in detail. For instance, there has been some 

 degree of post-Tertiary movement along the north side of the basin, 

 and the exposed beds have been found to contain saline strata which 

 exactly simulate beds deposited in continental inclosed lakes or 

 play as. It is difficult to reconcile this with the hypothesis of long 

 marine occupation of the trough. In this and other directions Dr. 

 Blake's theory may need revision, but its essentials will probably 

 stand. In any case, it is apparent that both the topography and the 

 history of the Salton have been very different from that of the basins 

 previously discussed. The major factor has been, not varying 

 climate but a vagrant Colorado. This difference of history makes the 

 usual criteria of little value. 



The size and nature of the drainage basin, its mutilation by stream 

 decay, the probabilities of inflow or overflow, are here of little im- 

 portance. Of course, salt accumulation is quite possible either by 

 the evaporation of marine water, the assistance of the river, or the 

 ordinary continental processes, but the problem is in no case one of 

 topography and'is therefore beyond the scope of the present paper. 



A word should perhaps be devoted to the delta of the Colorado.^ 

 This is a broad, alluvial plain, of no visible relief, and traversed by a 

 network of bayous. The position occupied by the divide between 

 gulf and basin is entirely indeterminate, and there is no rainfall to 

 develop it. The lower channel of the Colorado is exceedingly variable 

 and the delta is dotted with lakes and marshes, which are souvenirs 

 of its presence. So far as known, all of these are essentially fresh, 

 except some small ponds near the so-called Volcano Lake, and the 

 salinity of these is due to recent and present fumarole activity. One 

 of the lakes contains a considerable percentage of potash alum, which 

 will doubtless be developed when transportation and pohtical condi- 



1 For information concerning the delta I am indebted mainly to the papers of Dr. T). T. MacDougal and to 

 personal commxmication from him. 



