This report gives the principal results of an investigation of ground water in the Big Spring area, Texas. Big Spring, the county seat of Howard County, has an estimated population of about 16,000. It is situated on the Texas & Pacific Ry. and United States Highway No. 80 in western Texas, about 280 miles west of Fort Worth and along the boundary between the Edwards Plateau and the High Plains. Immediately south of the city is the bold escarpment of the plateau; to the north, west, and southwest lie the High Plains; and to the east lie the Osage Plains. The Edwards Plateau is capped by resistant limestones of Fredericksburg (Lower Cretaceous) age, which have a maximum thickness of about 160 feet. These limestones are underlain by sandstones of Trinity (basal Lower Cretaceous) age, which range in thickness from 60 to 100 feet and which form the principal water-bearing bed of the area. The High Plains are underlain in most places by a varying thickness of silt, clay, sand, and gravel, chiefly of Tertiary age. The Osage Plains are underlain chiefly by Triassic redbeds, which in general form an uneven floor beneath the Cretaceous and younger formations in the High Plains and Edwards Plateau. Beneath the Triassic redbeds is a great thickness of Permian rocks, which in parts of the area contain thick beds of rock salt. Over a large part of the plateau the Cretaceous rocks appear to be fiat lying but actually dip so as to form a northwestward-trending syncline. However, in places the rocks have slumped to form depressions or sinks, which serve as collecting basins for the water from the Trinity sand. As both Triassic and Cretaceous rocks are involved in the deformations, it is believed that they .may have been formed as a result of the solution and removal of the Permian salt by circulating ground water. Two of these sinks have been well known for several years. One of them, usually called the city park sink, is about 2 miles south of Big Spring, and the other, usually called the section 33 sink, is about 6 miles southeast of the city. These sinks are nearly circular. They have a diameter of about 1 mile, and the maximum displacement of the beds is 200 to 300 feet. They serve as collecting basins for ground water drained from the Surrounding Trinity sand, and wells drilled in them yield as much as 300 gallons a minute, largely from the cracks and crevices in the Fredericksburg limestones. As the Trinity sand is mostly fine-grained, wells outside the sinks seldom yield more than 20 to 30 gallons a minute. For many years the water supply of Big Spring and most of the water used there by the Texas & Pacific Ry. Co. has come from wells in the sinks, supplemented by a relatively small supply pumped from well fields between them. It is estimated that the perennial yield of the sinks and intervening well fields amount to an average of about 450,000 gallons a day. For several years-the pumpage has been much more than that, and in 1937 it amounted to an average of about 1,000,000 gallons a day. A large part of the water has therefore come from storage, and as a result the water table in the sinks, where the draft has been greatest, has declined to lower levels each year. If the water supply needed by the city continues to increase at the normal rate, most of the remaining water will be exhausted from the sinks in a few years if no other supply is provided. Although in some areas, such as sees. 44 and 45, the rocks are slightly deformed, no deep sinks that are comparable with the city park and section 33 sinks were found on the Edwards Plateau. A large amount of water is stored in the Trinity sand in areas on the plateau south of the present well fields, but as the sands are fine only small yields can be obtained from wells in them. Near Lees, about 12 miles southwest of Big .Spring, is a structural depression or sink about 1 mile in diameter, which contains Cretaceous limestone that is probably fractured and which is overlain by Tertiary