GEOTECTONICS OF THE ESTANCIA PLAINS 



CHARLES R. KEYES 



Prefatory. — The Estancia Plains lie in central New Mexico. 

 They form the extreme northern portion of the vast Mexican table- 

 land. In length they extend a distance of 150 miles; in width about 

 30 miles. 



Previous to the year 1900 the Estancia Plains were regarded as 

 the highest and driest bolson east of the continental divide. For this 

 reason, if for no other, the underground-water possibilities of this 

 region offered a theme for consideration that was of great interest. 

 Large industrial interests made possible the investigations necessary 

 to decipher the geological structure. Three new lines of railway 

 were under construction across these plains and good water-suppHes 

 became a matter of prime import. 



General features. — Geographically the Estancia Plains are located 

 at the juncture of the four greatest physiographic provinces of our 

 continent: The Great Plains, the Rocky Mountains, the Mexican 

 tableland, and the Colorado plateau. There are within the borders 

 of the Estancia area three very distinct types of orogenic structures. 

 These are superimposed upon a general and very remarkable epeiro- 

 genic uprase. 



At the north and east is the Rocky Mountain type, illustrating 

 tremendous compressive action. Over the west and south the basin- 

 range type of structure is finely shown in the immense tilted block 

 mountains. In the west-central portion is the laccoKthic type, repre- 

 sented by four distinct dome-shaped masses which have spread apart 

 Cretacic strata. 



In the main, the geologic structure of the Estancia Plains is that 

 of a broad trough, but there are many interruptions and local defor- 

 mations (Fig. i). As compared with the structure of the Jornada 

 del Muerto^ farther south there is not nearly the regularity (compare 



I Water Supply Paper No. 123, U. S. Geological Survey, 1904. 



434 



