GEOLOGICAL SETTING OF NEW MEXICO 



CHARLES KEYES 

 Des Moines, Iowa 



The unique distinction which New Mexico holds in American 

 geology is that it is the meeting-point of four major and diverse 

 geographic provinces. Together these four provinces embraces 

 nine-tenths of the North American continent. Effects of general 

 land depletion under widely different climatic conditions are thus 

 rarely so strongly contrasted. 



Situated well within the boundaries of the vast southwestern 

 desert, the operations of the epicene geologic processes are rendered 

 the more conspicuous because of the fact that they are so very 

 different from those of the pluvial eastern parts of the country 

 with which most of us are most familiar. 



New Mexico is distinctly a mountainous country. Its orogeny, 

 however, is chiefly erosional rather than tectonic. Relief of the 

 area is characteristically that of a land of little rain. Facial 

 expression of the region is clearly not stream-corraded but wind- 

 abraded. Owing to the fact that the wind sweeps up its chips as 

 fast as it cuts them the magnitude of eolic erosion is at first difficult 

 to measure with any great degree of satisfaction. Except under 

 especially favorable conditions definite figures cannot always be 

 given. Only when a desert chances to have, somewhere within 

 its boundaries, remnants of old peneplains highly uplifted may 

 the extent of regional depletion be closely estimated. As do moist 

 lands under the influences of stream activities, so arid regions soon 

 develop strong contrasts of surface relief under wind scour. Belts 

 of weak rocks are soonest worn down, leaving the hard rock masses 

 protruding as mountains 



In a region of uniform fiat-lying strata the relief contrasts are 

 not always marked. When, however, there are rock beds of great 

 thickness, alternating hard and soft members, with close-patterned 

 mountain structures as in the arid lands of western United States, 



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