Road Trip To The Boundary Waters (14)
In Search of Deep Time
Our outfitter for the Boundary Waters canoe trip is located in Winton, Minnesota, just outside of Ely. The fastest route from Sioux City, Iowa would take about eight hours. I never take the fastest route because the fastest route is usually the most boring. And the two side trips I had planned would keep me off major highways most of the way. So I added three additional hours. Still plenty of time to get to Winton before dark, even with a possible additional stop at Hibbing Minnesota, where Bob Dylan grew up. (Dylan chooses to pretty much ignore that fact. In his mind, he was raised in Greenwich Village.) But not enough time, unfortunately, to stop at the mighty fine Surly Brewing Company in Minneapolis, which I had last visited in 2014 on a road trip with my son, Andrew. (I refer to that trip as the Midwest Brew Tour.) I would still arrive long before Justin Rhodes, He had a ten-hour drive from his home in Champagne-Urbana, Illinois. But Justin couldn’t depart until noon because of teaching duties at the University of Illinois. He would arrive well after dark.
My first side trip was to Blue Mounds State Park. This place had two attractions for me, one of which was a remnant of tall grass prairie protected there. Tall grass prairies are among the most endangered ecosystems in North America. Once they covered 240 million acres extending throughout most of the Midwest from Eastern Kansas and Missouri to Manitoba. Iowa and Illinois were once almost entirely tall grass prairie, most of Minnesota as well. The tall grass prairie was largely destroyed by 1930, ploughed and converted to farmland, or overtaken by human encouraged forests. By some estimates, less than 1% remains.
The tall grass in tall grass prairies is due to a combination of abundant rainfall and rich soils. In the Great Plains region as a whole, rainfall levels steadily decline as you move east to west, a combination of influences from the Gulf of Mexico and the Rocky Mountains. The high humidity of the eastern Great Plains reflects the influence of the Gulf of Mexico; the further west you go the less that influence. Conversely, the Rocky Mountains create a massive rain shadow effect on the western Great Plains that is reduced the farther east you go. That largely explains why short grass prairie dominate the western Great Plains, while tall grass prairie dominates the eastern Great Plains. The large area in between is the domain of mixed grass prairie. The soils of the eastern Great Plains are enriched relative to the west as well. A mixture of sand, silt and clay, called loam, ideal for the growth of grasses and forbs. Loamy soils hit the sweet spot for water retention and water drainage; they also incorporate abundant nutrients. Early settler soon recognized that this soil was well-suited for cultivation, with no need for irrigation..
These loamy soils only developed within the last 8,000 years, a gift of the massive continental glaciers. Everything the glaciers plowed up on their way south—most of it Canadian--was either transported further south by water flow from beneath the glaciers or left in great heaps of unsorted material called moraines at their southern margins. This earthen potpourri was sorted over the years to create the soils we find today in much of the Midwest.
Tall grass prairie is an apt name; some grass species grow to over nine feet, virtually all the grasses are three feet or more. In contrast the short grass prairie grasses near the Rocky Mountains are generally 18” or less. The diversity of grass species also exceeds that of the short grass prairies. You might think of tall grass prairies as the rainforests of grasslands.
Bison once roamed all prairie types, but other animals were more restricted. Pronghorns, for example, were prevalent in short grass and mixed grass prairies but absent in tall grass prairies. Nor will you find a jackrabbit in the tall grass. Prairie chickens, on the other hand, require it.
The area of grassland preserved at Blue Mounds is small, and all the more precious for that. A trail from the parking lot took me uphill to an overlook. The cause of the elevated landscape was my second reason for visiting Blue Mounds State Park—the rocks. I have a longstanding infatuation with old rocks. By old I mean more than one billion years.
You won’t find many such rocks in California. But I frequent two places in the state where they do exist: The Ivanpah Mountains in the Mojave National Preserve, and the Black Mountains of Death Valley National Park. Most other rocks of this vintage in California are also in the eastern Mojave Desert*. Why? Because the basement of the eastern Mojave, unlike the basement under any other part of California, is a craton. If you find a rock over 1.5 billion years old anywhere in the world, chances are you are standing on a craton, the oldest and most stable parts of all continents. Cratons are the nuclei for all subsequent continental growth by way of younger rocks. The basement under Blue Mounds State Park is adjacent to craton, called The Superior Craton, the largest craton on earth.
Most of the Superior Craton is in Canada, comprising the basement for the eastern third of that country, and extending well into the High Arctic region. In the United States the Superior Craton is the basement for most of Minnesota and the eastern Dakotas. In Canada you don’t have to look hard to find large exposures of the Superior Craton, called the Canadian Shield. In The United States however, the craton is mostly buried under miles of sediments and younger rocks. Among the few places in the United States where the Superior Craton surfaces is northeastern Minnesota (including the area around the Boundary Waters) and the Upper Peninsula of Michigan. The craton also peaks out a in a couple of locations in southwest Minnesota.
The Blue Mounds rocks, called Sioux Quartzite, were made from the sandy southern shores of the Superior Craton, just as the Medicine Peak Quartzite that challenged me so during my hike in the Snowy Mountains was made from the sandy southern shores of the Wyoming Craton, both transformed from sand to quartzite at about the same time by a series of massive collisions. (For more on these two cratons, around which much of North America was constructed, see the appendix.)
My next stop was about one hundred miles to the northeast as the crow flies. But I took the scenic root, which probably doubled that. Along the way I began noticing patches of tall grass prairie--strips more like--on the sides of the road. West of the Rockies, the plants growing alongside a road are usually weedy invasive species that can tolerate conditions the native species can’t. In Minnesota though, things were quite different. Rather than excluding native plants, the roadsides seemed to function as sanctuaries for native grasses. Saved from the plough. It gladdened my heart.
My destination was a small city called Morton. This was a last-minute call. Or perhaps last night is more accurate. In my hotel room in Sioux City, I scanned the internet for a second possible side trip. I came across an excellent essay by Max Dresow, about an interesting place in Morton. It was posted on this website just over two weeks before (http://www.extinctblog.org/extinct/2024/8/17/minnesota-gneiss). It’s a fun read.
What got my attention was his discussion of the Morton gneiss (pronounced nice). At 3.55 billion years of age, the Morton Gneiss was once thought to be the oldest rock on earth, but that baton has been passed several times since. But the Morton Gneiss is the oldest rock in the United States. Put another way, 3.55 billion is three thousand five hundred and fifty million rears. For perspective, if one sheet of printing paper (.01 mm thick) represents one year. Half a billion (500 million years) would stack to a height of 500 meters. Now multiply that by seven—by conservatively rounding off 50 million years-- to get the height of the stack for a 3.5-billion-year span, which is 3,500 meters, or about 11,500 feet. That’s a lot of printing paper. If you were backpacking in the Sierras at that elevation, you would be well into the alpine zone. I find that awe-inspiring **.
If not for the directions garnered from the Dresow essay, I might not have found the location, called the “Morton Gneiss Natural and Scientific Area”. As instructed, I parked in a hotel parking lot and switched out my flip flops for hiking boots. There was no trail, but I was prepared for that and proceeded uphill, through a bit of tall grass prairie and into some shorter stuff as I neared the rocks. From the top of the rocks I could see the hotel and a highway, not what you would call scenic. Beyond the highway to the horizon, it was thick with trees. I could only imagine the unbounded prairie that was the former landscape.
The Morton Gneiss is not charismatic in the raw, especially when covered with lichens as it mostly was. But cut and polished the gneiss is enchanting: swirling pink, gray and black colors in chaotic flow, with white accents (https://www.mnopedia.org/multimedia/close-morton-gneiss). Cut and polished slabs of Morton gneiss were especially coveted for building adornment during the Art Deco period (1920s-1930s). Examples can be found from Seattle to Brooklyn; The Haupt Fountains in Washington D.C. are made from two enormous blocks of Morton Gneiss. (They frame the south entrance to The Elipse, courtesy of Lady Bird Johnson.)***
I lived for several years in the Fort Greene neighborhood of Brooklyn, less than a mile from another example of the way Morton Gneiss was used in architecture. It was called The Williamsburg Savings Building, but now known as the Clock Tower Building by locals. It was long the tallest building in Brooklyn and still one of the most beloved. Having done geology tours of Manhattan buildings,**** I was primed to notice the attractive stone used to veneer the first six feet of the Clock tower building. I probably touched it. But I had no idea then, how much history I was touching.
Appendix
1.8 billion years ago there was no continent to the south or east of the Superior Craton Nor was there anything south and west of the Wyoming Craton (Except the Mojave Craton). Areas that we now call the Northeast, the Southeast, most of the Midwest, the South, the Southwest, the West below Wyoming, and the Pacific Coast did not yet exist. Nothing where the state of Maine is, or Pennsylvania, or Florida, or Texas or Nebraska, or Illinois, or Colorado, or Arizona, or California or Washington, and all states that lie between.
On the southwestern shore of the Superior Craton, eroded sand accumulated offshore, then consolidated into sandstone, then further transformed—through metamorphism—into quartzite. The original offshore sand deposits, from which the quartzite derives is dated as roughly 1.7 billion years of age. The sand deposits off the Wyoming Craton from which the Medicine Peak quartzite derives are older, that is, eroded off the craton earlier, about 2.2 billion years ago. But both were transformed into quartzite at about the same time because of massive collisions with large island archipelagos, called the Yavapai Province that stretched from Wyoming to Ontario, Canada. During the collision the sandstones off both Wyoming and Minnesota got squeezed and buried to depths of high temperature and pressure where they metamorphosed into quartzite. The Sioux quartzites of Minnesota were unearthed, that is uplifted to the surface, quite recently (geological timescales), the Medicine Peak quartzites have a longer history on the earth’s surface.
Unlike the Sioux quartzite, the Morton Gneiss is part of the Superior Craton. It originated as granite, that is magma that cooled below the earth’s surface. During the formation of the Superior Craton from smaller Cratons the granite was repeatedly subjected to the depths and temperatures sufficient to change the original granite into Gneiss. The Morton Gneiss eventually at even greater depths and temperatures that transformed into a migmatite, as indicated by the swirling patterns. These patterns develop when the gneiss begins to melt. If completely melted it would become granite again. In the partially melted state, the pink swirls could be considered granitic.
Notes
*A strip of the Mojavia Craton, was sliced off in the Garlock Fault Zone, and transported west to become part of the Transverse Ranges, including the San Gabriel Mountains and the San Emigdio Mountains. You can find 1.8 billion year old rocks in these mountains as well, if you know where to look.
** I asked the Google AI how tall would one billion sheets of .01mm printer paper be. The error was easy to spot because the logic was spelled out:
A standard sheet of paper is .01 mm (right)
One million sheets would be 130 meters high (WTF: .01mm x 1 million = 10 meters)
Therefore 1 billion sheets would be 1,000x taller (correct) = 130,000 meters (wrong because of the first step)
According to the Google AI one billion stacked sheets of paper would be equivalent to a 43,333 story building (roughly 27 miles). I know LLM AI hallucinations are a problem for text prompts. But this was a simple math hallucination, not least in bringing the number 3 into the equation, which requires only the numbers 1 and 0. It also had a problem converting millimeters into meters. The message here is a healthy skepticism for AI hype, especially LLMs such as the Google AI and Chat GTP.
***The National Park Service should be ashamed of their description of the Morton gneiss from which the Haupt Fountains are made. They call it 3.5 million year old granite. 3.55 billion years ago it was 3.5 million year old granite!
****Manhattan geology tours of the rocks used for building materials are fascinating. You learn what they originally were and from whence they were quarried, among other things. Central Park also has some fascinating geology, including huge isolated boulders—called erratics--that were transported by glaciers over a thousand miles from where they originated in Canada.