Big Spring. -- This spring produces an average flow of 276 million gallons of water per day and has had measured peak flows of 800 million gallons of water per day. It has been calculated that a daily average of 175 tons of calcium carbonate (CaCO3) is removed from underground in solution through Big Spring. As a result, in one year the total volume of cave openings increases by 30 feet x 50 feet x 1 mile or 7,920,000 cubic feet.

 Ozark National Scenic Riverways contains more than 134 miles of clear spring-fed streams, hundreds of caves, and superb scenery. It is located in a geologically and hydrologically complex area, along the Current and Jacks Fork Rivers, that has received little previous attention from earth scientists.

The geology of the area is classified as karst terrain, characterized by dissolution-induced sinkholes, caves, and underground drainage. Bedrock consists mainly of dolomite and lesser amounts of sandstone and chert, interrupted locally by knobs of volcanic rhyolite that form a scenery of picturesque low mountains.

The spring system in this area is world class and unparalleled in North America. The Ozark region contains the three largest single-conduit springs in the United States, as well as numerous other major springs, which issue hundreds of millions of gallons of water per day. During peak flow, Big Spring alone produces over 800 million gallons of water per day. The area is truly one of America's natural resource treasures.

The Ozark Riverways area lies immediately south of the world's largest lead/zinc mining district -- the Viburnum Trend (Mississippi Valley-type ore deposits) -- and has geologic characteristics similar to those to which Viburnum Trend mineralization is attributed. Federal land in the area has been heavily explored in the past and is presently being explored by mining interests. The National Park Service, U.S. Forest Service, Bureau of Land Management, Nature Conservancy, Missouri Department of Conservation, many environmental groups, and local citizens are all keenly interested in the hydrogeology of the region, especially as it might pertain to potential mining activity. (text courtesy USGS)

Geology Tour of Ozark National Scenic Riverways

For more information go to http://pubs.usgs.gov/factsheet/fs50-97/.

Very detailed map of geology of Eminence / Two Rivers area. You'll need to use the magnify tool to read the text of this as the scale is very large. (.pdf file)