Additional exposure of the rhyolite is found in Blue Creek Canyon, where Oklahoma Highway 58 cuts through the Slick Hills. Tabular intrusions of granite and plutons of hydrous gabbro exploited the boundary between the layered complex and the rhyolites. The granites, collectively named the Wichita Granite Group, vary slightly in composition and texture. The granites form the peaks and highlands in the eastern Wichitas and the isolated peaks of the western Wichitas. Some are equigranular, but most are porphyritic. The Mount Scott Granite is the most extensively exposed Wichita Granite. It forms the topographic feature from which it takes its name, and it is distributed throughout the northern half of the wildlife refuge. Dark rounded alkali feldspars, typically one centimeter or less in diameter, dominate the porphyritic texture of this rock. SiO2 levels in this granite range from 72.8% to 75.8%. Relatively small and compositionally distinct plutons, known as the Roosevelt Gabbros, are found in the eastern and central Wichita Mountains. Like the layered complex, these are dark rocks. Unlike the layered complex, they contain appreciable amounts of biotite, a mineral that forms in magmas with elevated dissolved water. One of these bodies, the Mount Sheridan Gabbro, is exposed in roadcuts at Meers and underlies the Mount Scott Granite on the north side of the wildlife refuge. Weathered gabbroic soils are thicker and support more vegetation than those generated on weathered granite, so the tree line on the north side of Mount Sheridan approximates the contact between the Mount Sheridan Gabbro and the Mount Scott Granite. Geologic relationships suggest that the granites and gabbros intruded at depths no greater than half a kilometer in the crust. Minor uplift ensued, and magmatism concluded with the intrusive emplacement of subvolcanic features: rhyolite and diabase dikes. These are poorly exposed, with the exception of a large diabase dike in the Mount Scott Granite revealed during the recent widening of Oklahoma State Highway 49, just west of Interstate 44. Following the cessation of magmatism, the region subsided and was inundated by a shallow sea, resulting in the deposition of detrital sediments followed by carbonates. The change marks the local expression of the Sauk Unconformity. The light-colored rocks exposed in the Slick Hills are lower Paleozoic marine sediments, and are equivalent to those exposed in the Arbuckle Mountains, 100 km to the east. During the Pennsylvanian Period (330–290 million years ago) the region was subjected