The Roswell artesian basin is in the Pecos Valley in southeastern New Mexico. The investigation, which covered a period of three years, 1925 to 1928, was made for the purpose of determining the available supply of artesian and other ground water within the area. The geologic formations of the region are of the Carboniferous (Permian series) and Quaternary systems. The Permian rocks consist of three units-an upper unit composed chiefly of clay, shale, and sand; a middle unit composed chiefly of limestone; and a lower unit composed chiefly of red beds, gypsum, and anhydrite. Most of the artesian water is obtained from the limestone beds of the middle unit, which has been designated the Picacho limestone.
Originally the area of artesian flow comprised 663 square miles; but largely on account of heavy draft upon the artesian reservoir, it decreased to 499 square miles in 1916 and to 425 square miles in 1925. The area irrigated by water derived directly or indirectly from the reservoir amounts to about 60,000 acres. The annual quantity of water derived from wells is about 200,000 acre-feet, and the total discharge at the surface from all sources is about 250,000 acre-feet. Recharge to the reservoir is derived from precipitation that falls on a catchment area of 4,000 square miles west of the artesian area.
In 1927 a law was passed by the State of New Mexico declaring underground waters to be public waters and subject to appropriation. This law was declared invalid because of a technicality, and in 1931 a new law was enacted, which furnishes a definite basis for the future regulation of ground waters in the area.
The investigation leads to the conclusion that no new land should be placed under irrigation with artesian water, but that the development of shallow ground water should be encouraged. The present decline of the artesian head is slight in comparison with that in earlier years, and there is ample evidence to show that the reservoir annually receives large quantities of recharge and that with proper conservation it will never be completely exhausted.
