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 structure of the Gulf Coastal Plain, dip east-southeastward at an angle a little steeper than the general slope of the land surface.The lowest strata cropping out in the experimental watershed are part of the Wolfe City member of the Taylor marl and consist of about 110 feet of sandy marl containing

North Grape Creek quadrangle is south of the Llano region and is mostly in the broad Pedernales River basin. A few outliers of the Edwards Plateau are present in the western part of the quadrangle.