The Blacklands Experimental Watershed, a hydrologic research project of the Soil Conservation Service located about 15 miles southeast of Waco, Texas, is underlain by marls and chalks belonging to the Taylor group of the Gulf series of the Cretaceous system, which, in conformity with the general

The Ellenburger of Texas was first defined as a marine limestone formation of Cambrian and Ordovician age (Paige, 1912), but recently it has been subdivided into several formations and the term Ellenburger given group status (Cloud and Barnes, 1948).

Stonewall quadrangle is south of the Llano region and is in the marginal portion of the Edwards Plateau where much of the plateau surface has been destroyed by erosion.