Central Oregon has its own history of vulcanism. Mt. St. Helen's is only one of the more recent examples. I collected some obsidian from the slopes of Mt. Shasta in Northern California quite a few years back; I eventually gave it to my brother for his rock collection.

My brother recently had some rock from a farm in West Central Illinois assayed to prove or disprove an old legend about a silver mine. While the location of the mine is of course lost, the rock assayed out for both silver AND gold: you'd need to move and smelt a fairly large sized hill for the gold, but only half of that for the silver. It was decided not to pursue the minerals not only for economic reasons, but also the prevent a wild, mad gold rush into the farmlands of Illinois. Chicagoans flooding the area every Fall to "hunt deer" are bad enough!