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Field Trip: Duluth and the Upper Midwest

Weekend trip, Fall 2007

This was a field trip related to a Petrology course (GEOL 320). We learned the geologic history of the upper Midwest by observing outcrops near Lake Superior. Far from simply being a lake, Lake Superior is what remains of a time when North America almost split apart. Also in the area are remnants of tiny continents which slammed together to join a growing North American continent billions of years ago. This field trip was in association with the University of Minnesota-Duluth.


Tilted beds at Thomson Dam. There are no mountains in Wisconsin today. However, folded, tilted rock lie this provides evidence of mountains that long ago eroded away. The rounded holes in the rocks are places in which organic matter was at one point trapped. Later the organic matter dissolved out, leaving a hole.

northern lake

University of Minnesota-Duluth's Dr. Peterson discusses intrusions into basaltic rocks on Thompson Hill, the highest point around Duluth.

imbricated beach

A rocky beach along Lake Superior. Waves align flattened stones into a pattern called “imbrication.” After a lake or river has dried up, a geologist can tell ancient wave directions from the angle of the imbrication.


Review and recap at professor Tim Flood's house. We’re recording notes in our fieldbooks. A well-kept fieldbook is a geologist’s most important asset. Notes, observations and measurements are recorded for later reference. After all, what is important is what the rocks tell us - not what our vague recollection of the rocks tells us.

The sun finally breaks out, giving a great end to a great weekend.