CHAPTER V. 

 THE FLUCTUATIONS OF THE OTERO SODA LAKE. 



Variations in the level of lakes without outlets are universally recognized as one of 

 the easiest and most accurate methods of determining changes of climate. The well-known 

 monographs of Gilbert and Russell on Lakes Bonneville and Lahontan have shown that 

 during the glacial period the inclosed salt lakes of Utah and Nevada expanded, apparently 

 by reason of the same increase of precipitation or decrease of temperature which caused 

 the formation of the vast continental glaciers of northeastern America and northwestern 

 Europe. Further researches have proved that other salt lakes, not only in the arid South- 

 west of the United States, but tlu-oughout Asia, expanded similarly. Many of the old 

 lake basins, however, even in America, have not been accurately described as yetj and in 

 most of them little attention has been paid to evidences of minor fluctuations since the 

 last great expansion, which presumably took place synchronously with the last or Wisconsin 

 advance of the ice-sheet. Evidences of such minor fluctuations exist in various places, 

 one of which, the Otero Soda Lake, will be described in this chapter. Unfortunately in 

 this case, as in almost all others, we have no means of assigning exact dates to the various 

 stages of the lake. The only North American lakes where that is yet possible, even in the 

 most imperfect degree, appear to be those of the group immediately surrounding the City 

 of Mexico. They will be considered later, in a chapter devoted to Mexico. Meanwhile 

 we shall direct our attention to the minor fluctuations of the Otero Soda Lake and to the 

 accompanying formation of large expanses of gypsum dunes. We shall find that these 

 indicate that the change from the climate of the last glacial epoch to that of the present 

 does not appear to have proceeded by regular steps according to the old supposition. On 

 the contrary it seems to have been marked by pronounced pulsations. The minor strands 

 apparently do not mark mere stages of retrogression, but distinct periods of advance 

 separated by times when the water fell to decidedly low levels. 



Before discussing the features which bear on our immediate problem of recent climatic 

 changes, a short description of the Otero Basin in general will be in order, partly to give 

 the setting of what follows, and partly because this region has been discussed relatively 

 little. My study of the basin in the spring of 1911 was made in company with Mr. E. E. 

 Free, who at that time was engaged in an investigation of potash deposits on behalf of 

 the Bureau of Soils of the United States Department of Agriculture. I have drawn freely 

 on his observations and on the results of his work.* I take pleasure in here expressing my 

 thanks for his courtesy. 



The Otero Basin lies at an altitude of a little over 4,000 feet between two ranges of 

 fault-block mountains in the central part of southern New Mexico. The mountains run 

 north and south, and may be considered as disconnected continuations of the eastern 

 portion of the Rockies. The eastern range has an altitude of about 9,000 feet in the 

 Mescalero portion near the Otero Lake, while farther north in Sierra Blanco, or Capitan, it 

 rises to 13,000. The range is bounded on the west— that is, on the side toward the basin— 

 by a steep fault scarp. At the top lies the maturely dissected plateau described in the pre- 

 ceding chapter on the physiographic form of the land. Toward the north the plateau 

 rises into the well-dissected slopes of Sierra Blanco, while toward the east it falls off gradu- 

 ally to the Staked Plains of eastern New Mexico and western Texas. With these portions, 



* E. E. Free: The topographic features of the desert basins of the United States. Bui. 54, U. S. Dept. Agr., 1914. 



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