Jeff, that's a great list of sites that definitely have some old silver coins waiting for someone to find them!
Just wanted to share a quick story that your post reminded me of. My Mother grew up on a farm in western Wisconsin. I remember as a kid about a story her mother, my grandmother told of a small county fair that was held every year on a local farmer's property.
She recalled that there was a small pond on the property that a band would float out on a raft and play music throughout the entire fair. I never found out where it was located and regret that to this day!