As part of a broader research program to examine domestic source rock reservoirs, the Gulf Coast Petroleum Systems project of the USGS Energy Resources Program drilled a research borehole into Late Cretaceous mudstones in McLennan County, Texas, including the Cenomanian-Turonian Eagle Ford Group. A comprehensive wireline geophysical logging suite and over 600 ft of continuous core were obtained to advance the understanding of the stratigraphy, rock and fluid properties, burial history, and depositional environment of these uncompacted and thermally immature Eagle Ford source rocks. Geophysical logs were calibrated with geochemical core data to characterize mineralogical variability and petrophysical characterization of the mudstones in the USGS Gulf Coast #1 (GC-1) West Woodway study wellbore, as disseminated in Burke et al., 2020. Results of that research quantified total organic carbon content as well as total volumes of carbonate, siliceous minerals (e.g., quartz and feldspars), and clay minerals in the Eagle Ford Group and underlying units, and was used in conjunction with the comprehensive suite of geophysical logs to evaluate properties such as organic richness, mechanical integrity, and formation brittleness. Ongoing research into mudstone source rock reservoirs is vital for revising geologic models that serve as the foundation for resource assessments, and are referenced as source rock analogs for other similar petroleum systems in the U.S. and around the world.