The Western states are full of old mines, and Gold, Silver, and Copper mine maps for most Western states in the USA are planned for inclusion on this site.  The list of planned or active states includes:

Mineral wealth comes from mines, and everything you have in your life came from a mine or a farm, originally, followed by a factory and a road. It may not be obvious, but even economic or industrial resources such as gravel, gypsum, sand, or natural gas (the list is huge) make up all that you depend on every day.

For the adventurer and prospector, however, nothing has quite the same lure and excitement as precious metals! Gold, Silver, and Copper are especially interesting, in that they can also often be hunted with a metal detector by the casual professional. Additionally, the large economic and societal impact of precious metals means that seeking out and exploring the regions around old mines (it is strongly recommended you don’t enter old mines without a qualified professional!) will also provide many opportunities to discover and explore old ruins and signs from the past as well.