The study of the geohydrology of the Sparta Sand is the initial phase in the investigation of the geohydrology of the Claiborne Group. The thicker sections of the Sparta Sand lie along the axes of the Mississippi embayment and Desha basin. The area of maximum thickness, 1,100-1,200 feet, is in Claiborne and Warren Counties, Miss., and Madison Parish, La. Local thickening or thinning over some structures indicates structural movement during Sparta time. A sand-percentage map prepared from data derived from interpretation of electric logs indicates that the Sparta Sand was deposited as a delta-fluvial plain complex in Arkansas, Louisiana, and Mississippi. This complex shows a text-book example of a well-developed channel pattern. The delta-fluvial plain complex probably resulted from an ancestral Mississippi River system. In most of Texas the sand-percentage map shows a pattern suggestive of offshore or near-shore bar deposition. A map of the maximum sand-unit thickness shows the development during deposition of an interlacing channel pattern in Arkansas, Louisiana, and Mississippi. In the channel areas the maximum thickness of the sand units may be as much as 350 feet; in the inter-channel areas the maximum thickness is generally less than 50 feet. Coefficients of permeability and transmissibility for the Sparta Sand vary widely in localized areas. In the channels and area of Arkansas, Louisiana, and Mississippi, data suggest that the coefficient of permeability increases with an increase in maximum sand-unit thickness. These permeability values which depend on sand unit thicknesses, were used to prepare a map showing the transmissibility of the total sand thickness of the Sparta Sand in Arkansas, Louisiana, Mississippi, and eastern Texas. The data on the map show a close relation between channel development and high transmissibility values. The Sparta Sand is recharged by infiltration of water from precipitation on the outcrop, by leakage from other aquifers, and by seepage from streams. Natural discharge from the Sparta Sand takes place primarily by leakage through the overlying and underlying confining beds. In Texas, west-central Louisiana, and southeastern Mississippi the direction of flow of ground water is down the regional dip toward the gulf coast geosyncline. In most of Arkansas, Louisiana, and Mississippi the regional flow is toward the Mississippi River alluvial valley. In the channel-sand area of Arkansas, Louisiana, and Mississippi the ground-water flow is governed by changes in transmissibility, which in turn reflects the lithology. A study of the ground-water chemistry indicates that the areas of higher transmissibility have lower concentrations of dissolved solids than the areas of low transmissibility. On the basis of anion ratios, the waters of the Sparta Sand are grouped into three chemical provinces: the bicarbonate water province, the chloride water province, and the sulfate water province. The dissolved-solids content of waters from the Sparta Sand is closely related to the lithologic framework of the Sparta Sand area. Differences in water chemistry are attributed to regional differences in the rates of ground-water movement. Interpretation of the data suggests that the channel deposits have undergone a higher degree of flushing by fresh water than the inter-channel deposits.