Tatum dome, Lamar County, Mississippi, site of the Salmon atomic explosion of Project Dribble, is a roughly cylindrical salt stock having a slight overhang in the upper 2,500 feet. Diameter of the stock at 2,500 feet subsea is about 4,200 feet; top of the stock at 1,230 feet subsea is nearly flat. The salt consists of alternating bands of halite and anhydrite-rich halite; the bands are nearly vertical and several inches wide. In the upper 50 feet, banding is less steep, and the halite is purer and very coarsely crystalline.

Anhydrite caprock, extending umbrella-like over the salt stock, is almost entirely dry hard rock containing some fractures; its upper few feet is gypsiferous. Cavernous, brecciated, calcite caprock containing strontianite and celestite overlies the anhydrite; it contains comparatively fresh water.

Above the caprock is "false cap"--thin calcareous pyritized sandstone and fossiliferous limestone (probably early Miocene)--overlain by slightly arched beds of unconsolidated silty clay and sand (Miocene), 450 feet thick.

Data indicate that artesian water moves into the calcite caprock from the abutting Vicksburg Group (Oligocene); it then percolates slowly upward into shallower fresh-water aquifers.

Beds flanking Tatum dome are structurally disturbed. Tertiary beds in the shallow rim syncline have normal regional thickness. Aquifers around the dome contain fresh water as deep as 2,000 feet; saline water occurs in the Eocene Cook Mountain Limestone and in beds below.

Salmon was a 5-kiloton coupled atomic detonation centered at a depth of 2,700 feet in the northeastern quadrant of the dome.

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