Hummmm.... Maybe bullets that missed the last prospectors to hit that area? Just kidding of course. If the lead is in the area and you're finding other signs then I'd think it's a safe bet that there's gold as well. But I'm not a dredger so what the heck do I know? I'd be happy with enough water to pan with in this area!
Guess you can feel good about pulling that lead out of the stream anyway. Chances are someone drinks water from that source and now there's less lead to get into the water supply
I was looking at lead weight belt weights not too long ago and was shocked at the prices. Save that lead, at the very least you might come across somebody that wants to buy it from you.
I'd say send that picture to the California and Oregon legislators but it would probably cause them to stop all hunting and fishing too, instead of seeing one of the many good aspects of gold dredging.