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The Upper Peninsula of Michigan
Guest Column by GeoT

Dateline: 07/11/00

The residents of area code 906 in Michigan's Upper Peninsula (UP for short) are proud of their identity and they sell T-Shirts stating just that! Geographically, it looks like it belongs to Wisconsin (and some say it should), but because of economics it became part of Michigan ­ we'll see why. There has been "talk" of the UP becoming the 51st state, sometimes with a smile, and sometimes not!

The Upper Peninsula is an exposure of the crust protruding between three of the Great Lakes. The rock of the western UP is considerably older than that of the eastern part and contains metal ore minerals. That mineral wealth is the reason this land belongs to Michigan. Iron is one of them. More of those banded iron deposits of the Precambrian ­ the Marquette, Menominee, and Gogebic Ranges this time. As a result of the settlement of the Toledo War between Michigan and Ohio, the Upper Peninsula became part of Michigan. Industrialists from Detroit would benefit greatly as a result. The younger rock of the eastern section dips southward into the Michigan Basin and continues circling southwestward through eastern Wisconsin into Illinois and Indiana. A section of this is the same rock sequence that Niagara Falls flows over. In Illinois, we use that Niagaran Series dolomite as aggregate for construction in Chicago!

But there is another metal up this way that attracted attention too. Back in Precambrian times, the world was very different that the one we know today. Massive flows of lava were produced in this region ­ so massive they caused the earth's crust to sag beneath their immense weight. This sagging formed the synclinal basin presently occupied by Lake Superior. Modification by Pleistocene ice further deepened and widened this basin to its present configuration.

Lake Superior is the world's largest freshwater lake. Early explorers could not believe the Great Lakes were fresh water ­ way too big for that they thought. Superior is said to be the deadliest of the Great Lakes (but they all can be very unforgiving!). Many shipwrecks have occurred on or near the coast of the Upper Peninsula. Recall the wreck of the Edmund Fitzgerald on November 10, 1975. The great size of Lake Superior means that storms producing strong gales can create gigantic waves. Great distance to safe havens near the coast, hazards, bad weather, and navigation problems can lead to disaster. Such was the case with the Fitzgerald.

Striking into Lake Superior from the Upper Peninsula is a small peninsula called Keweenaw. It is an Ojibway name meaning: "the place we go around." This peninsula was created by the eruption of lava to the northwest. As that area sank under the weight, (and the removal of molten material from below) the southeastern edge, the Keweenaw Peninsula, was uplifted by folding, and faulting. The rock of the Keweenaw, bends below Lake Superior, and reappears as Isle Royale to the northwest.

Click here for a topographic map of the area (it will open in a new browser window)

Look at the arrangement of ridges and valleys. Landscape is based essentially on rock structure, weathering, erosion, and time. The ridges are more resistant lavas and conglomerates ­ the lower areas are less resistant. This area was subjected to intense glacial action. Look at the steeper southern slopes and the more moderate northern sides ­ this shows the rock dipping into the Lake Superior syncline. Lakes and swamps have developed in the poorly drained lower areas. Look at the pattern of roads and how they generally follow the less resistant, but flatter, inter-ridge areas. See how they traverse the ridges using the small stream valleys where they can?

With all this volcanic activity an interesting and valuable process of mineralization occurred: the emplacement of copper by hydrothermal solutions into some of the layers of lava, and the overlying conglomerates. The copper most likely originated in the upper layers of the mantle. Most of the time when copper forms, it combines with other elements, which require processing to remove. Not here. This is native copper. Metallic copper. It fills small, and sometimes large, gas holes in the vesicular lavas, and invades the overlying conglomerates, -- cementing and even replacing some of the pebbles with metal! One copper boulder shipped to Detroit for display weighed two tons! It is in the Smithsonian today and is known as the Ontonagan Boulder.

What a find! No wonder the industrialists from Detroit had no intention of letting this piece of real estate go to someone else! Isle Royale also has copper deposits (which is why the U.S.-Canadian border swings north of it). The U.S. wanted the copper, and got it, as part of the settlement of the Revolutionary War. Benjamin Franklin was aware of the copper deposits and had the boundary drawn accordingly. Native Americans were mining and using these deposits long before the Europeans arrived ­ so the copper didn't need to be "discovered" ­ just taken over!

The heyday of copper mining in the UP was between 1847 and 1887 when Michigan led the nation in copper production, but production peaked in 1916 when 135,000 tons were produced. Several mines and towns stretched along a narrow zone right through the middle of the peninsula. Copper ingots were shipped from small ports on the coast to eastern factories. The United States was becoming electrified and the need for copper was great. The city of Calumet on the Keweenaw was among the world's first cities to install electric streetlights and trolley cars.

Michigan continued to produce copper until 1997 when the last operation, the White Pine Mine, was closed. This mine was working a shale unit that contained finely divided copper particles ­ not the amygdaloidal lavas or conglomerates of those earlier mines. Many tons of shale produced only a relatively small amount of copper.

Mining is known as a "Boom and Bust Industry" but in the 1800's, and continuing into the 1900's the Keweenaw was booming -- big time!

It's a great place to visit today and see the old towns and mines. Then, return to the coast of Lake Superior and look along the beach for igneous and metamorphic rocks smoothed by the surf. Beautiful specimens! (Paint them with clear coat and they look wet all the time). And, maybe, even enjoy beach fire made of driftwood at night!

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GeoT is a long-time high school geography teacher from Illinois. In addition to geography, he enjoys railroads and model railroads, old Oldsmobiles, and gardening.

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