Geology of Yellow Hill Quadrangle, Brewster County, Texas

The Yellow Hill Quadrangle is between the Bofecillos, Davis, and Chisos volcanic centers of Trans-Pecos Texas. Tertiary volcaniclastic deposits occur only as small outliers on downthrown sides of faults. Erosion has removed the thin Tertiary section to expose the 1365 m section of Cretaceous limestones, which are mostly biomicrite (wackestone). Tertiary diabase sills have extensively intruded upper Cretaceous limestone, but intruded the entire interval from the upper Comanchean Buda Limestone to the middle Oligocene Mitchell Mesa Tuff, inclusive. The sills form part of a belt of mafic sills which extends into Mexico as much as 70 km to the southeast.