A summary of the occurrence and development of ground water in the southern High Plains of Texas

Abstract

The Southern High Plains of Texas occupies an area of about 22,000 square miles in northwest Texas, extending from the Canadian River southward. about 250 miles and from the New Mexico line eastward an average distance of about 120 miles. The economy of the area is dependent largely upon irrigated agriculture, and in 1958 about 44,000 irrigation wells were in operation. The economy of the area is also dependent upon the oil industry either in the form of oil and gas production or in the form of industries based on the production of petroleum. The Southern High Plains of Texas is characterized by a nearly flat land surface sloping gently toward the southeast at an average of 8 to 10 feet per mile. Shallow undrained depressions or playas are characteristic of the plains surface, and during periods of heavy rainfall, runoff collects in the depressions to form temporary ponds or lakes. Stream drainage on the plains surface is poorly developed; water discharges over the eastern escarpment off the plains only during periods of excessive rainfall. The climate of the area is semiarid; the average annual precipitation is about 20 inches. About 70 percent of the precipitation falls during the growing season from April to September. Rocks of Permian age underlie the entire area and consist chiefly of red sandstone and shale containing numerous beds of gypsum and dolomite. The Permian rocks are not a source of water in the Southern High Plains, and any water in these rocks would probably be saline. The Triassic rocks underlying the Southern High Plains consist of three formations of the Dockum group: the Tecovas formation, the Santa Rosa sandstone. and the Chinle formation equivalent. The Tecovas and Chinle formation equivalent both consist chiefly of shale and sandy shale; however, the Santa Rosa sandstone consists mainly of medium to coarse conglomeratic sandstone containing some shale. The formations of the Dockum group are capable of yielding small to moderate quantities of water in many parts of the Southern High Plains; however, in practically all places the water is rather saline and probably unsuitable for most uses. The Cretaceous formations in the Southern High Plains consist of several formations of the Trinity, Fredericksburg, and Washita groups. The rocks underlie a large part of the southern part of the Southern High Plains; they consist of sandstone, shale, and limestone, the sandstone and limestone being the principal water-bearing units. In a few places where the Cretaceous rocks appear to be in hydraulic connection with the overlying Ogallala formation, moderate quantities of water are obtained, particularly from the limestones. Locally the Cretaceous rocks may be important aquifers where other water is not available, but they generally do not constitute a large source of water for irrigation or municipal use. The Ogallala formation of Pliocene age is the principal aquifer in the Southern High Plains of Texas; it supplies practically all the water used for all purposes. The formation is continuous throughout most of the Texas part of the Southern High Plains and extends into New Mexico. The .formation consists chiefly of sediments deposited by streams that had their headwaters in the mountainous regions to the west and northwest. The Ogallala formation rests unconformably upon an erosional surface of the underlying Triassic and Cretaceous rocks. The Ogallala consists of beds and lenses of clay, silt, sand, and gravel; caliche occurs as a secondary deposit ,in many places in the formation. In general the Ogallala is thicker in the northern part of the area; the thickness ranges from 400 to 500 feet in central Parmer, west-central Castro, and southwestern Floyd Counties to a knife edge where the formation wedges out against outcrops of the older rocks.