region in McCulloch, San Saba, and Lampasas counties. In this area, Marble Falls Limestone, Smithwick Shale, and lower Strawn Group are well exposed. The strata of the lower Strawn Group are truncated by an erosional unconformity that is overlain by much younger Cretaceous strata. The succession of Carboniferous strata within and adjacent to the Llano Uplift records the pronounced subsidence and filling of the adjacent Fort Worth Basin by the westward progradation of delta and associated fluvial systems from the uplifted Ouachita Mountains to the east. The Chappell Limestone and Barnett Shale represent episodic early Carboniferous inundations of the Llano region followed its submergence and formation of a carbonate platform within which the Marble Falls Limestone accumulated as a lateral equivalent to deeper water Smithwick Shale. As the Fort Worth Basin deepened and sank in responses to the Ouachita Orogeny, Smithwick Shale was deposited on former sites of Marble Falls sedimentation within the Llano Uplift region. In the deeper part of the Llano region, basin-fill shale and submarine fan deposits that form the lower Strawn Group accumulated. As the basin filled during the remainder of the Carboniferous and Permian, fluvial-deltaic sediments and associated shallow marine continental shelf deposits of the upper Strawn, Canyon, and Cisco group accumulated within the Fort Worth Basin. Mesozoic The only Mesozoic rocks that are known in the Llano region are those of the Cretaceous system. Throughout Triassic and Jurassic periods, the Llano region was eroded. The accumulation of Triassic, terrestrial red beds of the Dockham Group may have reached to the western edge Llano region. However, they were eroded back to its present position and underlying strata eroded during the Triassic and Jurassic in response regional tilting and uplift. By the time that the regions of the Llano Uplift was slowly covered by Cretaceous sedimentary deposits, it had been reduced by erosion to a low relief erosion surface termed the Wichita paleoplain. What little research has been conducted on the Wichita paleoplain estimates that as much as of relief exists on this surface cut into the underlying strata. During the Cretaceous, this surface was progressively buried by the accumulation of fluvial and coastal sediments of the Trinity Group and later by the Walnut, Comanche Peak, and Edwards formations. Cenozoic Erosion that has occurred since the withdrawal of Cretaceous seas has resulted in a topographic inversion. As a result, the oldest and structurally highest rocks tend