Silver Cliff Roadcut Along Highway 61
February 12, 2007
Follow U.S. Highway 61 along the North Shore of Lake Superior, through Silver Cliff Tunnel, and as you emerge from the tunnel you'll see this magnificent wall of rock! Click on image to enlarge. Terry Boerboom of the Minnesota Geological Survey mapped out the area and provided the following description:
"The red lines on the above photo are the limits of a wide fault gouge filled with pink zeolite minerals; the green line is the margin of the Silver Creek diabase, and the blue line is a highly irregular flow contact between two andesite flows. The flows have been slightly metamorphosed by the sill. This roadcut exposes the base of an approximately south-dipping diabase (Silver Creek diabase) that has intruded the surrounding volcanic rocks. On this end of the tunnel, the volcanics are andesitic flows; on the other end, on top of the diabase sill, is a flow of ophitic basalt. Also, there's a wide zeolite-filled fault gouge that's slightly oblique to the flow contact."
You can park nearby and walk along the old roadway, the entire length of the tunnel, where you're greeted with a spectacular view of Lake Superior about 100 feet (30 m) below the cliff. The birds and wildflowers (in summer) aren't to be ignored either. This road-cut and tunnel are both quite amazing. In fact, they won an award from the U.S. Department of Transportation (Federal Highway Administration) for excellence in highway design. See link below. Photo taken on August 1, 2006.