Vista of Buda, Eagle Ford, and Austin Formations, Terrell County

One charge of the U.S. Geological Survey’s Energy Resources Science Center is conducting field work to
better understand the distribution of hydrocarbon source rocks as input to USGS oil and gas
assessments. This 2015 image is a view to the south-southeast of rocks exposed along an unnamed
draw near Antonio Creek, Terrell County, Texas. The Buda Limestone is exposed along the draw (right
side of image behind prickly-pear cactus. In the far-left distance, the dissected hill is topped by the Austin
Chalk. Sandwiched between the Austin Chalk and the Buda Limestone is the gray-colored mudstones of
the Eagle Ford Shale, a major hydrocarbon source rock in the subsurface of South Texas. Historically,
observations made in the field are used to map and reconstruct the spatial distribution of an ancient
ocean and shorelines in this part of Texas during the Cretaceous Period.