I know the area very well, as I lived there once. From experience and others I know, you would do quite well around lake Melones. I have picked it up myself as well as many others I have known. Another interesting area, is the housing subdivision of Gold (something) estates in Columbia. There is a creek there, and the gold and crystals are there. You may actually be surprised that homeowners would more than let you explore if you are respectful, and offer a 50% split! Between Jamestown and Table Mountain areas there are landowners who are kind and would let you pan or detect. Talk to them, knock on their doors, and give it try. We allowed folks to do this when I lived there.