Formed through volcanic activity over 1.4 billion years ago nothing is left of these mountains but the roots. They are center of the Missouri mining region yielding; iron, lead, barite, zinc, silver, manganese, cobalt, nickel, granite, and limestone.
Mountains in this range include; Taum Sauke Mountain, Bell Mountain, Proffit Mountain, Pilot Knob Mountain, Hughes Mountain, Goggin Mountian, and Lead Hill Mountain. The elevations range from 500 Feet to 1,772 feet. Taum Sauke Mountain is the highest peak in the range, and the highest point in the state, with an elevation of 1772.
Hughes Mountain contains a good example of columnar jointing in igneous rhyolite, the same process that formed Devils Tower. The Columnar jounting in this area is called the Devil's Honeycomb.
Unlike the rest of the mountainous areas in the Ozarks the Saint Francois Range was formed by true volcanic activity where as mountainous areas in the rest of the Ozark Platue was caused by errosion. The volcanic activity that formed this mountain range is also thought to be the geological cause of the Ozark Platue.