Uplift and erosion followed, as the layered complex is unconformably overlain by the extensive lava flows of the Carlton Rhyolite Group. The rhyolites are an brown-red to orange porphyritic rock with 5–10 mm orange-colored alkali feldspar crystals. Most of the rounded hills on Fort Sill are made of this rhyolite, including Medicine Bluffs. 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.