Saint Francois Mountain Range
The Saint Francois Mountains, a range located in southeast Missouri, is an outcrop of precambrian igneous rock mountains rising over the Ozark Plateau. It is belived that this range is the oldest exposed igneous rock in North America. The range is often misspelled as St. Francis to match the local pronunciation.
Formed through volcanic activity over 1.4 billion years ago, nothing is left of these mountains but the roots. By comparison, the Appalachians started forming about 460 million years ago, and the Rockies a mere 70 million years ago — when the Appalachians started forming, the St. Francois range was already twice as old as the Appalachians are today.
Unlike the rest of the mountainous areas in the Ozarks, the Saint Francois Mountains were formed by true volcanic activity. The localized vertical relief observed in most of the Ozarks, a dissected plateau, was caused by erosion. The volcanic activity that formed this mountain range is also thought to be the geological cause of the uplift of the Ozark Plateau. Geologists talk of the "Ozark dome" wherein elevations and stratigraphic inclines generally radiate down from the Saint Francois mountains. These elevations may be the only area in the American midwest never to have been submerged, existing as an archipelago in paleozoic seas. Fossilized coral, the remains of ancient reefs, can be found among the rocks on their flanks.
The St. Francois Mountains are the center of the Missouri mining region yielding; iron, lead, barite, zinc, silver, manganese, cobalt, nickel, granite, and limestone.
Mountains in this range include; Taum Sauk 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 (167 to 540 meters). Taum Sauk Mountain is the highest peak in the range, and the highest point in the state, with an elevation of 1772 ft. (540 m).
Hughes Mountain contains a good example of columnar jointing in igneous rhyolite, the same process that formed Devils Tower. The columnar jointing in this area is called the Devil's Honeycomb.
A part of the Ozark Trail winds through parts of the St. Francois Mountains, including a popular section that crosses Taum Sauk and Proffit mountains.
See also
References
Unklesbay, A.G; & Vineyard, Jerry D. (1992). Missouri Geology — Three Billion Years of Volcanoes, Seas, Sediments, and Erosion. University of Missouri Press. ISBN 0-8262-0836-3.
