Recent work by the Minnesota Geological Survey permits the construction of a detailed structural map of the southeastern part of the State with contours drawn on the Jordan-Oneota contact. The major structure is not the “Twin City” syncline as mapped formerly (Trowbridge, 1934) but a series of gently pitching troughs, basins, and domes.

In the region of the Twin Cities approximately 2500 square miles are underlain by a roughly circular basin around whose margin the Jordan-Oneota contact occurs at an elevation of 700 feet above sea level. The bottom of the basin, outlined by the 450-foot contour, is broad and flat. The average dip is about 20 feet per mile. The Hudson-Afton anticline modifies the structure of the east margin. Along the south edge of the basin an east-west-trending anticline extends directly across the area formerly mapped as synclinal. The area south of this structural high is characterized by a downward warping that formed a broad, gently pitching syncline whose major axis extends from southern LeSueur County southeastward into Iowa. There are three minor dome-like structures and smaller folds on the east limb of the syncline. The elevation of the Jordan-Oneota contact rises from 200 feet above sea level in the region of Austin to over 1150 feet on the crest of a local high to the southwest of Winona. Faults occur along the valley of the St. Croix River north of Stillwater and along the Mississippi valley at Hastings and Red Wing.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.