. Mandan
Pit is a gravel pit full of rocks and sand that were carried from nearby
sources and deposited by ancient glaciers. Datolites, "float copper" and
few other interesting rocks can be found there assuming that you're able
to beat anyone to them that is. I hadn't had any good luck with that site
so far. Most datolites found there are heavily weathered (bleached), but
some colored ones had been found. There was a rumor of purple datolite
being found there.
