Bulletin 11—The Geology of the Organ Mountains
with an account of the geology and mineral resources of Doña Ana County, New Mexico,

By K. C. Dunham, 1935, reprinted 1980, 87 pp., 11 figs., 5 plates, 1 index.

From the introduction:

Doña Ana County embraces the southernmost part of the valley of the Rio Grande in New Mexico, together with a region of arid plains and abrupt mountain ranges. The most prominent topographic feature of this area is the north-south trending Organ range, lying to the east of the river. The county, including this mountain chain, exhibits a wide variety of geological phenomena, and has been the scene of mining operations for almost a century. It has nevertheless received very little attention from geologists, for while good reconnaissance studies of the geology and of the mineral deposits have been made, no part has previously been subjected to a detailed investigation. The principal object of the present report is to record the results of a detailed study of the geology of the Organ Mountains. In addi - tion, a general account of the geology of the county, based upon reconnaissances made by the present author, and upon the writings of former workers, is included, together with a special section on the natural resources of the region.

The work was carried out during the writer's tenure of a Commonwealth Fund Fellowship, and this condition made it possible to take a broader view of the geological problems than is normal in studies sponsored directly by the State Bureau of Mines and Mineral Resources. Part I of the bulletin, entitled "The Geology of the Organ Mountains" is intended as a contribution to geological science, and in it the history of the range, as determined from field mapping and laboratory studies, is discussed. Part II is devoted to a general summary of the geological features of the rest of the county, and serves as a background for the detailed study, and for Part III, in which the mines and quarries of the county are described. In Part III the application of the geological results to the exploitation of the mineral resources of the region receives special consideration.

Two seasons were spent in the field, from September 1933 to January 1934, and from August 1934 to January 1935. The Organ Mountains were mapped topographically and geologically on a scale of one inch to one mile. A more detailed map, on a scale of four inches to one mile, was made for the Organ mining district. In addition, certain areas were mapped on larger scales. (Plates II and III, and figures in text) . The map of Dona Ana County (Plate I) is based partly on the general map of the State, by N. H. Darton, and partly on studies by the present author. The period intervening between the field seasons was spent in laboratory examination of material from the area at Harvard University, and some months were also devoted to this work during the winter of 1935.