Paleozoic sedimentary rocks in the subsurface of the Black Mesa basin of northeastern Arizona include 0-800 ft. of Cambrian dolomite, sandstone, shale, and minor limestone, 0-300 ft. of Devonian dolomite and sandstone, 0-500 ft. of Mississippian dolomite and limestone, 0-500 ft. of Pennsylvanian redbeds and limestone, and about 1,000-2,000 ft. of Permian redbeds and eolian sandstone capped by 0-400 ft. of dolomite near the western edge of the basin. These rocks do not crop out, and only a few wells have penetrated them to date. Isopach and lithofacies maps show that in all Paleozoic systems the thick marine carbonate sections of northwestern Arizona and southwestern Utah pinch out, become more clastic, or interfinger with continental sedimentary rocks in the direction of the Black Mesa. At no time during the Paleozoic or Mesozoic eras was the Black Mesa a basin in the sense that it was the site of deposition of marine sediments significantly thicker than in surrounding areas. A structural basin was formed by differential uplift in Cenozoic time. When the entire Colorado Plateau was uplifted, the Black Mesa area rose 3,500-7,000 ft. less than the surrounding country. Possibilities for oil and gas discoveries in stratigraphic traps seem best in the northern and western parts of the Black Mesa basin, where a moderately thick Paleozoic marine section is present and where complex facies changes occur in rocks of several Paleozoic systems. Chances are poor in the eastern part of the basin, which lies on the western flank of the Defiance positive area, a structural high that persisted through much of Paleozoic time. In general, the Black Mesa basin has a much thinner marine sedimentary section than the nearby San Juan, Blanding (Paradox), Henry, and Kaiparowits basins.