THE PHYSIOGRAPHY OF MEXICO 1 



WARREN N. THAYER 

 Cincinnati, Ohio 



For one who approaches the study of Mexican physiography 

 for the first time, it facilitates matters considerably to acquire in 

 the very beginning a few. fundamental concepts, particularly as 

 regards the relations of the provinces of Mexico to those of the 

 United States. We are likely to regard the Mexican provinces as 

 ending abruptly on the north at the International Boundary, and 

 at the south along an irregular political line separating Mexico from 

 Central America. As a matter of fact, the Mexican physiographic 

 provinces extend well into the United States, the natural northern 

 boundary being in a general way the Pecos-Rio Grande, the escarp- 

 ment of the Colorado Plateau, and the southern terminus of the 

 Sierra Nevada Mountains. As thus bounded, Mexico, from a 

 physiographic viewpoint, includes those provinces hitherto described 

 for the United States under the names of Trans-Pecos Highlands, 

 Arizona Highlands, and Colorado Desert. 2 The natural southern 

 boundary is the isthmus of Tehuantepec. This excludes the states 

 of Tabasco, Campeche, Yucatan, and Chiapas, but physiographi- 

 cally speaking, these political divisions belong to Central America 

 rather than Mexico. 3 



All the topographic features included between these natural 

 boundaries, with the exception of a narrow strip along the Gulf 

 coast, may be traced back to a common feature which came into 

 existence in early Tertiary time, and for which Hill has suggested the 

 name "Cordilleran Peneplain." 4 This peneplain was made on the 



1 For complete bibliography see list of references compiled by me and published 

 in Mining Science, LXX, Nos. 1745-47. 



2 N. M. Fenneman, "Physiographic Boundaries within the United States," Ann. 

 Ass. Am. Geog., IV, PL 1. 



3 E. Bose, Guides des excursions, 10th Inter. Geol. Cong. Mex., igo6, XXXI, 15-16*. 



4 R. T. Hill, "Growth and Decay of the Mexican Plateau," Eng. and Min. Jour., 

 LXXXV, 681-88. 



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