76 C. K. KEYES INTERMON^T PLAINS OF THE AEID REGION 



Under normal conditions of a humid climate the three general plains 

 mentioned naturally would be regarded as representing as many different 

 peneplanation levels, as indeed Hill has already urged; but their pres- 

 ence on the border line of the t3^pically arid countr}^ suggests that all of 

 these plains, with the possible exception of the Mesa de Maya, should be 

 ascribed to desert-leveling instead of normal peneplanation. It is not 

 unlikely that the Mesa de Maya is also a plain produced by desert- 

 leveling; but assuming that it is not, and a true peneplain instead, gen- 

 eral desert-leveling alone must be regarded as having removed from the 

 plains a thickness of not less than 3,000 to 5,000 feet of rock materials. 

 It is also very suggestive that this is also approximately the present 

 heights of the desert ranges above the plains surface. This phase of the 

 subject is capable of much further elaboration. 



Eastern New Mexico is on the border of the humid and arid regions. 

 Whatever may have been the later activities of the geologic processes 

 under conditions of aridit}^, there seems to be good reason for believing 

 that there was in this part of the Southwest something of the nature of 

 a peneplain to start with, though its continuity may have been very much 

 broken on account of profound faulting and orogenic deformation. As 

 they now stand, it would hardly be proper to call either the general sur- 

 face of the tableland or that of any of the intermont basins peneplains, 

 in the strict meaning of that term. 



PLANATIOy INUEPEXDEyr OF SEALEYEL 



The fact that some of the bolsons of Xew Mexico were destructional 

 plains instead of constructional plains, as had been generally regarded, 

 was first personally impressed as early as 1902, after considerable de- 

 tailed investigation in regard to the underground water supplies of the 

 Estancia, Jornada, San Augustine, and other great plains of the region. 

 A 3'ear later the first evidences bearing on this subject were published. ^^ 

 The article in which these facts were presented was of the nature of an 

 advance paper taken from two more comprehensive reports on the "Geol- 

 ogy and underground water supplies of the Estancia plains," and on the 

 same general topic as relating to the Jornada del [Muerto.^* The first of 

 these memoirs discussed in considerable detail the action of the wind as a 

 leveling agent over broad areas and even as the chief agent in the excava- 

 tion of large hollows and minor lake basins in the arid region. 



During the following year opportunity presented itself to extend the 

 observations over the greater parts of Arizona, Texas, Oklahoma, and old 



15 American Journal of Science (4), vol. xv. 1903. pp. 207-210. 



" U. S. Geological Survey, Underground Water Supply and Irrigation Paper, no. 123, 



it\rz 



1905. 



