The Eau Claire Formation was formed during the Cambrian era and forms a cusp like trough through the middle of the State.  The Cambrian era formations are evidence of tidal flows and global flooding over the middle of the continent.  The Eau Claire formation is one of just a number of fining upward and coursing upward formations within the Cambrian era. Transition zones bound the Mt. Simon, Eau. Claire, Wonewoc, Lone Rock, St. Lawrence and Jordan Formations where the rock composition changes from course grained sandstone (Ex. Mt. Simon formation) to fine grain sandstone with large amounts of silt (Ex. Eau Claire formation).   The Cambrian sandstone shows no signs of fossil evidence although there is evidence of Biotrabation.
 
 
 

Mt. Simon Formation

Wonewoc formation with lesagage banding