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EXHIBIT D MINING PLAN Mining started in 1911 and consisted of both underground and surface workings. Several of the clay veins on the east side of the hogback and along the entire length of the hogback on this property were mined from underground workings; most of the stopes are still open to the surface. One area that was surface mined is now within the stockpile area on Map Exhibit D-1. When mining ceased in this area, a bare highwall (slope 1/2 to 1) was left that was approximately 220 feet long and 60 feet high. That highwall was buried under the stockpile area last year. Additional clay veins will be surface mined along the east side of the hogback. These veins are located in the Dakota Formation (see vertical section). At the mine site, the Dakota Formation dips at 55 degrees to the east. Three clay veins within the formation designated as H3, H4 and H5, (colored yellow in the vertical section), are considered mineable by the company. The lowest strata strata- graphically, which is also the furthest west strata of the Dakota Formation, is a competent sandstone and will become the mine highwall. Immediately above this sandstone strata are two of the three clays, the HS and H4. This HS is approximately 12 feet thick perpendicular to the hogback. The H4 clay, which is approximately 6 feet thick, was extensively mined from the underground and has only ramdom pillars left to recover. Separating the H4 and HS is the sandstone parting (colored red in the vertical section) approximately 1.5 feet thick. Above and perpendicular to the H4 is approximately 38 feet of sand- stone. The H3 clay, which is next in sequence, is approximately 15 feet thick. Above and perpendicular to the H3 is approximately 30 feet of sandstone and above these sandstones are clays of the Benton Formation. The Benton clays are not planned to be mined at this time. The final planned depth of the pit is approximately 130 vertical feet below the crest of the hogback. Because of the slope on the east side of the hogback the maximum depth of the cut will range from 100 to 30 vertical feet. The overburden to be removed between the H3 and H4 will consist of sandstone and the overburden to the east of the H3 would consist of sandstone and Benton Formation clays. If any additional mineable veins of clay are encountered during mining, they will be recovered as mining progresses. Mining will begin by stripping any available topsoil in advance of the areas to be disturbed. Topsoil in the areas to be mined is virtually non-existant due to the steep, rocky slopes; any topsoil that might be encountered will be stockpiled to the east of the mining areas. The permit boundary includes area for any such stockpiles.