I started reading my new book in earnest. It is Minnesota's Geology by Ojakangas and Matsch. I like it better than my old MN geology book, which is really too old, because it has more humor and human interest.
The first chapter is a briefing about geology in general with just a few specific Minnesota references. It starts out with an exciting version of how the Minnesota River formed, when a melting glacial lake overflowered and flooded through a valley, eroding it and revealing much older rocks. This may have occurred twelve thousand years ago. Some geological dates are mind-boggling; 12 thousand years doesn't seem that long. Or does it? Another fact that stood out is that Minnesota doesn't have any gemstones of significance. But collectors can find agates and other quartz minerals that are quite interesting.