Reddit reviews Roadside Geology of Minnesota

I can't speak for any specific trails or such, but I do recommend looking for the book Minnesota's Geology published by University of Minnesota Press. It is written by Dr Richard Ojakangas and Dr Charles Match, both former geology professors at University of Minnesota Duluth. It covers a lot of the interesting geology found in the state, with great coverage of the different bedrock types found throughout and how they relate to geologic history and Minnesota's place in it.

Here's an Amazon link to the book too: https://www.amazon.com/Minnesotas-Geology-Richard-Ojakangas/dp/0816609535

Another one you might like is called Roadside Geology of Minnesota, again by Dr Ojakangas: https://www.amazon.com/Roadside-Geology-Minnesota-Richard-Ojakangas/dp/0878425624

This would be a good book to check out IMO: http://www.amazon.com/Roadside-Geology-Minnesota-Series/dp/0878425624