The Geology of Minneopa State Park - webapps8

Geological history foundin Minnesota's parks—The Geology of Minneopa State ParkGEORGE A. THIELMinneopa State Park is located sixmiles west of Mankato in Blue EarthCounty where Minneopa Creek tumblesover two waterfalls. The name"Minneopa" is an Indian word meaning"Two Falls". The park lies alongU. S. Highway No. 169 andState Highway No. 60. Ithas facilities for picnicking,running water system, moderncomfort stations, a shel-Stateter and refectory.The most outstandingtopographic features in thepark are the waterfalls and the deepgorge, the walls of which are coveredwith a dense, mature stand of mixeddeciduous timber. This deep glenfollows an irregular course for a distanceof about half a mile where itjoins the valley of the MinnesotaRiver. Minneopa Creek, the streamthat has eroded the gorge, has itsheadwaters in the group of lakes nearCrystal Lake.GeologyThe creek flows northeastward in aGEORGE A. THIEL is chairman of the Departmentof Geology and Mineralogy at theUniversity of Minnesota• • •shallow valley across the uplandprairie, but where it approaches theMinnesota River Valley it has cutdownward through the glacial driftand into the underlying Cambriansandstones and shales.The fall escarpment atMinneopa Falls is caused byofthe Jordan sandstone. TheParks perpendicular fall of thewater is about 30 feet. However,before reaching thepoint where the water leapsover the cliff, the stream haseroded through a thickness of about15 feet of sandstone. At that depth itcomes in contact with a harder portionof the sandstone which has athickness of six to eight feet. Thesemore thoroughly cemented layers resistthe erosive action of the streamlonger than the underlying softer layersand thus produce the projectingshelf over which the water plunges.Number nineThe pool below the falls is in awalled amphitheater that rises about40 feet on each side. The walls arekept wet by the splash and spray51