There you go Roger. You had to be on the site, unless there is some other civilization nearby. Would be pretty random to hit a coin that was a completely random desert drop.
Slick way to clean those off is to rub damp baking soda on them between your fingers. Shines them right up and while it probably leaves microscopic scratches, you can't see them w/ the naked eye. If i really don't want to scratch them, i put them inside a wad of tin foil, and cover them with baking soda, then pour boiling water inside to cover them. Wait a few minutes and the tarnish transfers to the foil.
Way to go!
Zincoln