Hey CLevar, Looks like warhawk and I are on the same trail.
Seems like everyone up there has a hard time finding good knapping material.
The first thing that comes to mind is the Knife River flint of North Dakota. It's a beautiful material
and if you just Google it you ought to come up with all the info you need.
Right where you're at it seems Chert and Agate are about it. Because of all the glacial action up there,
I would try your gravel bars in the creeks and rivers. Nodules of the chert may have gotten washed out.
You would just have to sit there with your rock hammer and bust alot of rock until you find a piece that
looks like it might work. I know that may sound like a longshot, but it can be fun and there's really no
telling what you might find. The agate up there is beautiful, as you probably know, but it's hard stuff
and hard to find pieces large enough to use for knapping.
The silicified sandstone might be a good material, too. And it might have some nice fossils in it.
Here are a couple of links I found about Minnesota material; (I hope they work),
http://www.osa.admin.state.mn.us/documents/LithicWorkshop.pdfNotice on this next site that all the material listed is the same chemical composition, SiO2, which is the same for quartz.
Chert, flint, jasper, and agate all are chalcedony. The more pure, or white, materials are just called chalcedony.
But they are all basically cryptocrystalline quartz.
Not trying to get you sidetracked here, but I think it helps when hunting to know a little about the animal
you're hunting. Here's that other site;
http://www.mnsu.edu/emuseum/prehistory/minnesota/technology/lithics.htmlAnd here's the link to a fellow rockhound just north of you who has recently started knapping and hunting
for knapping material. Check out his site;
http://estevanrock.proboards.com/index.cgiAnyway, I hope this helps you some. And just remember, there's always empty beer bottles.
Best of Luck, Joe