Tatum salt dome, a subsurface feature in southwestern Lamar County, Miss., was formed by a salt stock, about 1 mile in diameter at the top, that has protruded through rocks as young as early Miocene in age. The salt stock is the medium in which an experiment using nuclear devices is proposed. The top surface of the salt stock, which has very little relief, is about 1,500 feet below land surface. Overlying the salt is an anhydrite caprock 400 feet thick which in turn is overlain by calcite caprock 50-150 feet thick. The sediments surrounding and overlying the dome have a regional dip to the southwest of about 40 feet per mile except where modified by Tatum dome and other structures.

Hydrologic Test Well 1, the first multiple-test well, was drilled about one-half mile northeast of Tatum salt dome, Lamar County, Miss, (fig. 1). It is at Atomic Energy Commission coordinates 12,273 No and 12,759 E., approximately 370 feet southeast of the center of sec. 12, T. 2 N., R. 16 W., at an altitude of 315 feet above sea levels Hydrologic Test Well 1 was drilled as part of the Public Safety Program, which requires determination of the geologic and hydrologic conditions that exist on and near the dome. The well is one of several test wells drilled or planned for exploration of hydrologic conditions at Tatum salt dome. The well was drilled by the Layne-Central Company, The depth, thickness, general characteristics, and stratigraphic sequence of the formations and aquifers are shown on figure 2, A detailed description of the drill samples, sidewall cores, and vertical cores is given in tables 1 and 2. The attitude and areal extent of the aquifers is being determined by relating the information obtained from this test well to information from other test holes, wells, and seismic data available in the Tatum dome area.

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