More pictures from Hughes Mountain. Columnar rhyolite (really a devitrified rhyolitic ash flow tuff) covered in lichen, with fiamme and flow banding.

Hughes Mountain is an igneous knob in the St Francois Mountains of southeastern Missouri, the product of intercontinental volcanism during the late Precambrian, roughly 1.5 billion years ago. Other notable spots within the St Francois Mountains are Elephant Rocks, Johnsons Shutins, and Taum Sauk Mountain.