Richard W. Ojakangas

Another in the Roadside Geology… series picked up at the 2013 GSA convention[/url]. The way it works out, most Minnesota “geology” is concentrated in the northeast corner of the state; everywhere else all the rocks are buried under up to 800 feet of glacial drift. Quaternary geology is somewhat more subtle than the hard rock variety; the Grand Canyon (for example) is breathtakingly obvious but recognition that there was an equally impressive meltwater lake (Lake Agassiz) that covered a good part of Minnesota, Ontario and Manitoba and contained more water than all the Great Lakes combined requires close attention to subtle terrain features (and thus is really not suitable for the “Roadside” approach; a Pleistocene beach terrace only a few feet higher than the surrounding terrain is not likely to draw gasps of wonder while cruising by on the Interstate). Still, the coverage of glacial geology is thorough and pretty interesting; in my college days the Pleistocene was pretty settled; there were four glaciations (Wisconsinan, Illinoisan, Kansan and Nebraskan in North America; Würm, Riss, Mindel and Günz in Europe; had to memorize all of them and their approximate dates for a Pleistocene archaeology class). Like a whole lot of other 1960s geology (geosynclines and cryptovulcanism), further research collapsed the neat explanations. The stages had been figured out by superposition; each new glacial advance would scrape away almost all the evidence of its predecessor; only around the limits of advance were there cases where more recent glacial features overlaid older ones. So if you found that a Wisconsinan age moraine overlapped older moraine somewhere, the older stuff was assigned to the “Illinoisan” glaciation, and so on for the other glacial periods. The catch was these superposition cases were rare and widely separated and the assumption that they were contemporaneous turned out to be unfounded once radiometric dating got into the act. By the time I was working in geology again, the Wisconsinan was still around but there were between 8 and 15 earlier periods and they no longer had convenient names; there are now up to 40 glacial advances depending on who’s counting. What’s more, resolution has become sufficiently good to distinguish individual “lobes” within a major glaciation; thus the Wisconsinan in Minnesota includes the Superior lobe, the Wadena lobe, the Des Moines lobe, the Labradoran lobe, the Red River lobe, and the Rainy lobe; the lobes are sometimes simultaneously active (advancing) but sometimes not, and sometimes one is advancing while another retreats. Roadside Geology of Minnesota covers all this thoroughly but there’s not much to see; I suppose there’s some comfort to be told that a particular linear mound off in the distance is the remnants of a Rainy lobe stagnation moraine but there’s not much to involve the casual geologist.


The glacial geology can be better appreciated from topographic views. The ultraflat land in the northwest corner of the state is Lake Agassiz lakebed, and Red Lakes and Lake of the Woods are remnants (as are Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, Cedar Lake in Manitoba and Lac la Ronge in Saskatchewan). At various times Lake Agassiz drained to the Arctic Ocean, Hudson Bay, the Atlantic, and the Gulf of Mexico; this last drainage route left the wide swath of flat terrain extending diagonally across the southern half of the state and now occupied by the Minnesota River, a classic example of an “underfit” stream – much smaller than its valley suggests (it was Glacial River Warren in the Pleistocene). Minnesota still has three drainage basins (to the Arctic Ocean via the Red River of the North, the Atlantic via the Great Lakes, and the Gulf of Mexico via the Mississippi) the triple point where the three connect is, again, pretty subtle. For this part of the state author Richard Ojakangas includes various historical tidbits to fill out the text; even so three quarters of the state take up only one quarter of the book.


There is, of course, a satisfactory amount of “real” geology in the northeast corner of the state, where the last glaciation conveniently scraped everything down to bedrock and didn’t leave a lot of ground moraine and outwash when it melted back. What’s there is pretty interesting indeed, including what were for a while the oldest known rocks in North American (since passed up by some in Wyoming and Ontario); surface traces of the Mid-Continent Rift; some nice Proterozoic greenstone belts documenting the very beginnings of continental drift; a Proterozoic suture zone; the Iron Range, and the Gunflint Chert where the first Proterozoic bacterial fossils were discovered (although the actual first discovery was made from Gunflint Chert outcrops in Ontario). Since major highways are sparse, the book provides a lot of get-out-and-walk investigations in this area, including mine tours and hikes along the Superior lakeshore.


Given the limitations of dealing with a state where much of the geology is Pleistocene, this is pretty well done. There are a lot of illustrations (sadly, many of the glacial geology pictures are of fresh roadcuts noted as “since grassed over”). I was a little disappointed in the lack of large scale geological background; it would have been nice to see some continental reconstructions from the Proterozoic illustrating how the continental collisions and rifting were supposed to work back then. To be fair, though, that issue is still unresolved so it might have been overly speculative for Ojakangas, and his reconstructions of Pleistocene glaciation episodes are well presented and very instructive. There’s an “Additional Reading” section which isn’t really a bibliography but is instead just what it says; additional reading for the layman geologist. I definitely want to do some more research on Glacial Lake Agassiz but will search for some more technical works.… (plus d'informations)

Richard Ojakangas is a native Minnesotan whose life has been spent in learning about and teaching Minnesota's geological history. He taught at the U of M in Duluth for over 30 years, and is the author of Minnesota's Geology, which is probably the definitive geology book on the North Star State.

That book, however, is not quite meant for the casual reader (although its less imposing than many other books of the type). Minnesota has lacked a Roadside Geology style book for too long. After years without one, Ojakangas has finally written a book for the non-scientist, the latest in the Roadside Geology series, the Roadside Geology of Minnesota.

It's been worth the wait.

After an introduction to the geological history of Minnesota (as you might expect, the Pleistocene, with its glaciations, gets a lot of space) as well as some basic geology to get those who avoided the rock science in high school or college, the book divides into several sections based on Geography. (Northeastern, Northwestern/Central, Southwestern, Southeastern)In each section, Ojakangas gives a general overview of the Geology of that area followed by the meat of the book, Road Guides.

There are plenty of photographs, maps and diagrams to elucidate the text and keep travelers oriented as they visit the various highlighted sites. I learned about plenty of sites that were just off of my route in previous travels that I will definitely visit with book in tow. I had no idea, for instance, of a beautiful beach of rhyolite pebbles lies just 3 miles north of Gooseberry Falls. I'd never heard of Chimney Rock, a spire of sandstone a few miles off of US 61 on the way south from St. Paul. In addition, I have an appreciation for places and locales I have seen, now having a better geological context for them. The composition and nature of Barn Bluff in Red Wing, for instance. I had no idea there's a fault that has shifted the layers on one side of it!

Armchair amateur geologists who buy the Roadside series of volumes will not want to miss this latest volume.I most especially recommend this book, though, for any and all Minnesota travelers interested in the physical geology of the state to buy the book, read it, and then take it with you on your next road trip to, say, Gooseberry Falls, or Winona, or the Boundary Waters, or Pipestone. I certainly will!… (plus d'informations)