Michigan Geology Gallery

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To go directly to a particular locale shown in this gallery, click on its name below:

- Baraga County (Upper Peninsula)

- Esrey Park (Upper Peninsula: Keweenaw County)

- Fayette State Historical Park (Upper Peninsula: Delta County)

- Houghton County (Upper Peninsula)

- Marquette County (Upper Peninsula)

- Pictured Rocks National Lakeshore

(Upper Peninsula: Alger County)

- Tahquamenon Falls State Park

(Upper Peninsula: Chippewa & Luce Counties)

- Warren Dunes State Park (Lower Peninsula: Berrien County)

2. Ah, Copper Country. Looking south along the Keweenaw Peninsula's western shore. Here basalt flows of the Lake Shore Traps dip westward, under the floor of Lake Superior. This basalt was part of innumerable lava flows that welled to the surface when this region was part of the Midcontinent Rift System, approximately 1.1 billion years ago. This episode -- it occurred long after the rise and fall of the lofty Penokean Mountains -- marked a time when the crust of ancestral North America was stretched, thinned, and fractured, perhaps as part of the breakup of the ancient supercontinent Rodinia. For a discussion of the plant community here, see Photo 1 in my Plants of Michigan Gallery.

5. A huge, 17-ton chunk of native (essentially pure) copper that was raised off the bottom of Lake Superior. It now resides on this dolly in the Quincy Mine and Hoist Museum in Hancock. Note how its upper side has been smoothed by the movement of sand and probably glacier ice, too. This mineral collector's vision of paradise is not "float copper" -- in other words, it wasn't hefted by a glacier from some other location. However, there are many other cases of ice sheets carrying Keweenaw copper to distant stations. One humble example is the piece of copper, about the size of a tennis ball, that I came across while leading a tour in a gravel pit west of Chicago. It had been buried for thousand of years in a deposit of glacial outwash, after having been transported 400 miles to the south.

12. The Upper Falls, Tahquamenon Falls State Park, in Chippewa County. Undoubtedly one of the most popular tourist spots in Michigan's Upper Peninsula, these roaring and majestic falls are relentlessly cutting through Cambrian-Period Munising Formation sandstone. This is a topnotch place to see the impact that the local plant communities -- particularly the coniferous trees of the North Country taiga -- have on the local hydrology. According to one old beer commercial, this is "The Land of Sky Blue Waters," but in fact this is The Land of Water That Suspiciously Resembles Liquid Shoe Polish.

13. One section of Tahquamenon's Lower Falls. The effect is not so awe-inspiring here, but their more human scale and their greater sense of roiling energy make the Lower Falls just as dramatic, in their own way. Once again, notice how brown the water is where it hasn't been aerated by a great deal of turbulence. This arresting color is not the result of some rogue paper mill or sewage plant upstream. The fallen foliage from untold thousands of conifers of nearby peatlands and swamps contributes a vast supply of tannic acid that darkens the water naturally.

7. The Route 41 pillow lavas are a type of slightly metamorphosed basalt known as greenstone. This rock is an very important constituent of the oldest surviving sections the Earth's crust. Large greenstone belts, made up of this rock and associated sedimentary rocks, alternate with more highly deformed gneiss belts to make up the ancient cores of the continents. This esoteric fact is not lost on one Michigan State Trooper, who stopped to invesigate me and one of my tour groups when we had pulled over to scrutinize this outcrop. As it turned out, the officer had been a Earth Science major in college, and we had an excellent geo-conversation with him. However, he did call us wimps for wearing sweaters and jackets when it was still a balmy 40 degrees Fahrenheit.

1. A roadcut of the purple and white-spotted Jacobsville Sandstone, along U.S. Route 41 just west of L'Anse. This distinctive sedimentary rock, once used extensively as architectural dimension stone, was often marketed as "Lake Superior Brownstone." (See Photos 10-12 in my Architectural Geology Gallery.) Originally thought to date to the Cambrian Period (ca. 560-505 million years ago), it is now known to have been deposited much earlier, in the late Proterozoic Eon, a little more than 1.0 billion years ago. It is found on the eastern half of the Keweenaw Peninsula, and also farther east, along the northern shore of the main part of the Upper Peninsula.

11. The magnificent Grand Sable Dunes, as seen from the Log Slide Overlook of Pictured Rocks National Lakeshore. The dunes of this most imposing section of the Upper Peninsula's Superior coast are perched -- in other words, they have been built up on preexisting glacial sediments. The net effect is that of great sloping walls of whiteness, extending almost four hundred feet to the turquoise and indigo expanse below. As I learned years before, as a youth insistent on getting down to the water's edge, this is another one of those places where, to crib from Virgil, the descent is easy and the labor is in the return. Actually, the descent is quite a chore, too, for those who experience vertigo.

3. The Silurian Escarpment, strikingly evident along the western shore of Upper Michigan's Garden Peninsula, at Fayette State Historical Park. The park is a partially restored nineteenth-century iron-smelting center. The rock unit that makes up the escarpment's face is the Hendricks Dolomite Formation, which was deposited approximately 420 million years ago in a shallow, tropical sea. The Escarpment circles the the Great Lakes Basin, and is visible as well in Wisconsin, near Horicon Marsh and also on the Door Peninsula -- which, incidentally, is the direct, southward extension of the Garden Peninsula. The ridge then parallels the southern shore of Michigan's Upper Peninsula, and extends through Lake Huron country to Niagara falls in western New York state.

4. Another view of the thin-bedded Silurian dolostone at Fayette State Historical Park. Mixed in among the bone-white flagstones on the beach are dark chunks of smelting slag, the resolidified remains of molten rock, glass, and charcoal that were the waste product after the iron was removed from its ore. It may not sound very appealing, but slag is often quite beautifully iridescent and distinctively textured. And, come to think of it, it's both a genuine archaeological artifact and an anthropogenic (manmade) geological deposit. .

14. The surf and southeastern shore of Lake Michigan, at Berrien County's Warren Dunes State Park. The term "lake" is here a bad but customary use of language. This in fact is an inland sea, or, as the early Frech explorers called it, a Sea of Sweet Water. Lake Michigan and its four sister lakes constitute one fifth of the planet's supply of fresh water, and their fate is uncertain in light of runaway human population growth and our ever-increasing demands on this most precious natural resource. The Lake Michigan basin probably began as a south-trending river valley largely cut in soft, Devonian-Period shale. The valley was then dramatically widened and deepened by Pleistocene-Epoch glaciers.

6. This and the photo at right are views of one of America's most famous set of roadcuts, approximately seven miles west of downtown Marquette on U.S. Route 41. The western half of the Upper Peninsula has all sorts of ancient, Precambrian rock units, but this exposure contains ancient pillow lavas dated to the Archean Eon. They're at least 2.5 billion years old. As its name suggests, this rock structure resembles a heap of very uncomfortable pillows and forms when red-hot lava comes into contact with water. Most pillow lavas, including these, are thought to originate on the ocean floor, either at spreading centers, volcanic island arcs, or hot spots.

8. The now inactive iron mine in the Upper Peninsula town of Republic. The open pit at right, originally 600 feet deep, has filled with ground water. The ore quarried here was hematite (an iron oxide) contained in an ancient banded iron formation. This unusual sedimentary rock type is often abbreviated to "BIF" by geologists.

9. A BIF boulder. This big specimen, placed near the Republic Mine's public viewing platform, shows the beautiful banding pattern: specular hematite, a dark glittery silver, alternates with blood-red jasper, a semiprecious mineral. Banded iron formations are thought to be indicators of the Earth's early, low-oxygen atmosphere. Unlike most other rock types, BIFs are no longer being deposited; some 1.9 billion years ago their production ceased when the atmospheric oxygen level rose to about 15% of its current level.

15. Looking the other way at Warren Dunes State Park. This is one small section of the great hills of sand that adorn the Lake Michigan coast of the western Lower Peninsula. Because the prevailing winds are from the west and the northwest, the sand delivered to this shore is driven inland into great piles. On the opposite shore of Illinois, the same winds tend to sweep the sand back into the lake.

10. Welcome to the Archean Eon. Roadcuts along Michigan 95 north of Republic reveal ancient Archean granite at least 2. 5 billion years old. This host rock was subse-quently invaded by dolerite dikes associated with continental rifting in the Superior Region early in the Proterozoic Eon, about 2.3 billion years ago. In this photo, the coarse-grained granite (off-white when fresh) is a light pinkish brown due to weathering; the younger dolerite is black.

Would you like to learn more about the geology of this diverse and fascinating state? Check out my Courses, Tours, and Lectures Pages for educational events focused on the Earth science of Michigan.