Mach Report This Comment
Date: January 15, 2013 09:47PM

See that red splotch (Precambrian) down toward the SE corner, that's a huge volcanic eruption that formed the St.Francois mountains.... over a billion years ago.

St. Francois Mountains
The "top" of the Missouri Ozarks is in the St. Francois Mountains, an area composed of the oldest rocks in the state. The highest elevation is 1,772-foot Taum Sauk Mountain. These peaks were formed by the erosion of igneous rocks which originated as volcanic eruptions and molten intrusions approximately 1.3 to 1.5 billion years ago.