DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP HA-3SO UNITED STATES GEOLOGICAL SURVEY GROUND WATER IN OGALLALA FORMATION IN THE SOUTHERN HIGH PLAINS OF TEXAS AND NEW MEXICO By James G. Cronin INTRODUCTION trate the continuity of the principal ground-water reservoir between the two States. The Ogallala Formation of Tertiary (Pliocene) age is the principal aquifer in the Southern High Location and Description of the Area Plains of western Texas and eastern New Mexico. This heavily pumped aquifer supplies practically The Southern High Plains of western Texas all the water used for irrigation, municipal, in­ and eastern New Mexico is the southernmost part dustrial (except oil-field repressuring), and do­ of the High Plains section of the Great Plains mestic purposes. Physiographic province (Fenneman, 1931,p. 10). Although the ground water in the Ogallala It is the High Plains area south of the Canadian Formation in the Southern High Plains is common River, known locally as the South Plains. The to both Texas and New Mexico, the State laws name "Llano Estacado," given to the area by the concerning ownership of the water are different. early Spanish explorers, is less often used. The New Mexico statutes provide that all under­ The Southern High Plains has a total area of ground waters of the State belong to the public about 32,OCX) square miles in western Texas and and are subject to appropriation for beneficial eastern New Mexico. The peninsula-like part of use (Reynolds, 1961, p. 79). Under conditions the area, about 4,000 square miles, extending specified in the law, the State Engineer may de­ eastward from Potter and Randall Counties clare certain areas as underground water basins through Carson and northern Armstrong Coun­ in which the State Engineer has jurisdiction over ties, Texas, between the Canadian River and the drilling of wells. The approximate boundaries Prairie Dog Town Fork of the Red River, is not of two such basins in New Mexico are shown on included in this atlas. In general, the included the maps. In Texas, the landowner owns the area is rectangular, averaging about 190 miles underground water. Under a law passed by the from north to south and about 150 miles from Texas State Legislature in 1949, underground east to west. water conservation districts may be formed with The region is essentially a plateau, bounded the authority to make rules and regulations for on the north by the deep valley of the Canadian the conservation of ground waters, such as rules River and on the east and west by prominent governing the minimum spacing of wells, and escarpments rising as much as 300 or more feet rules for the prevention of waste and contamina­ above the stream-eroded lower lands. The top tion of fresh water, and other practices for the of the escarpment, which is usually capped with conservation of ground water. The approximate caliche, is referred to as the "caprock." On the boundaries of two underground water conserva­ south, the Southern High Plains merges without tion districts in Texas are shown on the maps. a sharp physiographic break into the Edwards Plateau. Purpose and Scope of This Atlas Canyons have been cut into both the eastern The purpose of this atlas is to show in con­ and western escarpments. The larger and more venient form the current information about the striking are along the eastern escarpment, where ground-water reservoir in the Ogallala Forma­ erosion is more effective because of the surface tion in the Southern High Plains of Texas and slope and heavier rainfall. New Mexico. The maps show the saturated thick­ The surface of the plains is remarkably flat ness of the Ogallala Formation, the approximate throughout much of the area and, gently undulat­ altitude of the base of the Ogallala Formation, ing in the remainder. Features of r eli ef that the approximate altitude of the water table in the interrupt the flat surface are numerous shallow Ogallala Formation, and the approximate decline depressions or playas, sand dunes, and small of the water table since the beginning of large- stream valleys. An exception to the flat surface scale withdrawals for irrigation. The maps illus­ is the Portales Valley in eastern New Mexico which is a major topographic feature of the the eastern boundary of the Pecos River drain­ plains. age basin in the area of this atlas. Runoff is gen­ The amount and direction of the maximum erally channeled to the southeast, away from the slope of the plains surface vary somewhat in escarpment, because of the general slope of the different places, but in general the surface slopes land surface. A few small intermittent streams east-southeasterly from the escarpment on the may divert some water into the Pecos River, but west in New Mexico at rates ranging from about the amount is probably very small. 8 to 20 feet per mile. The steeper slopes are The Portales Valley extends from near Krider, generally in the western part of the area. New Mexico, east-southeastward through Por­ Undrained depressions or playas ranging from tales, into west-central Bailey County, Texas. a few feet to 50 feet or more in depth and from The valley is about 30 miles wide in the vicinity a few hundred feet to a mile or more in diameter of Portales and about 250 feet deep (Theis, 1932, are characteristic of the topography in the South­ p. 103). ern High Plains. The drainage area of the playas Sand dunes and areas of deep sandy soils, may range from a few square miles to as much where present, givtf the plains surface a billowy as 50 square miles, and during periods of heavy appearance. The location of one of the most ex­ rainfall, runoff collects in the depressions to tensive sand dune areas is shown on the maps. form temporary ponds or lakes. Some of the Other sand dune areas are generally in the south­ larger and deeper playas contain "alkali" or ern and southwestern part of the area. "saline lakes." The high mineral content of the water results from concentration of the salts by Climate evaporation. The Southern High Plains of western Texas Stream drainage is very poorly developed and and eastern New Mexico has a semiarid climate. stream dissection is very light. Long shallow Factors which characterize the climate are: Low valleys, almost devoid of tributaries, follow the average annual precipitation, which varies in general slope of the land surface at widely spaced amount annually and seasonally and in geographic intervals. These valleys form the headwater distribution; a high rate of evaporation; low rel­ reaches of three major rivers: the Red, the ative humidity; high average wind velocity; Brazos, and the Colorado. The drainage area of warm to hot summer days followed by cool the intermittent streams that occupy the valleys nights; and moderate winters with some severe is limited to the stream valley and to narrow cold spells. The average annual snow fall is belts of sloping land adjacent to the valley. Sur­ light; the snow usually melts within a few days. face water accumulating in the streams ordinar­ Hail occasionally damages crops in local areas. ily flows for only short distances before being Dust storms occur often, especially during the lost by seepage or evaporation. months of January through June. Tornadoes oc­ The Southern High Plains area generally does cur during late spring and early sumnier. not contribute to streamflow east of the eastern Climatological data from records of the United escarpment except during rare periods of ex­ States Weather Bureau are summarized in table cessive rainfall. The western escarpment forms 1 for several stations in Texas and New Mexico TABLE 1. U.S. Weather Bureau climatological data for the Southern High Plains of Texas and New Mexico Station Altitude, feet Average annual Mean annual Evaporation, above mean sea precipitation, temperature, inches level inches degrees F Amarillo 3,590 19.21 57.5 Big Spring 2,538 14.19 64.5 Crosbyton 3,037 18.67 60.0 Midland 2,854 12.41 64.0 Caprock 4,335 12.09 Clovis 4,280 17.14 57.3 '104.15 Hobbs 2,615 13.71 62.2 Melroee 4,599 12.97 57.5 Portales 4,004 15.43 58.2 2 92.52 Ragland 4,900 17.27 1 Statwn located 13 mites north of Clovu 1 Station located 7 miles west-northwest of Portales. for the period 1951-60. These data indicate that lished maps pertaining to the geology and hydrol­ the precipitation decreases from east to west ogy of the Portalee Valley area by Mr. Sherman and in general from north to south. E. Galloway and of Curry County, New Mexico, by Mr. Robert L. Borton were modified and Economic Development adapted for use in preparing this part of the atlas. The economy of the Southern High Plains of Texas and New Mexico is based largely on the GROUND-WATER GEOLOGY OF THE presence of fertile soil, an abundance of ground SOUTHERN HIGH PLAINS water, and large quantities of oil and gas. Dur­ The rocks that crop out the Southern High ing the early period of development, beef cattle Plains range in age from Permian to Holocene. was the principal product; later, dry-land farm­ Older rocks are present in the subsurface, but ing became important. In the 1930's and 1940's, they are not important as sources of ground large-scale irrigation began and large oil and water. gas fields were discovered. Approximately 5,000,000 acres are now irri­ Rocks of Permian to Cretaceous Age gated (1967) from an estimated 50,000 or more Rocks of the Permian System underlie all of wells, of which about 300,000 acres and about the Southern High Plains and are the oldest rocks 4,300 wells are in New Mexico.