Geotectonics of the Estancia Plains

Abstract

Prefatory.-The Estancia Plains lie in central New Mexico. They form the extreme northern portion of the vast Mexican tableland. In length they extend a distance of 150 miles; in width about 30 miles. Previous to the year 19oo 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-supplies 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 epeirogenic uprase. At the north and east is the Rocky Mountain type, illustrating tremendous compressive action. Over the west and south the basinrange type of structure is finely shown in the immense tilted block mountains. In the west-central portion is the laccolithic type, represented 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 deformations (Fig. i). As compared with the structure of the Jornada del Muerto, farther south there is not nearly the regularity (compare