These are links to US government sites that deal with geology. The US government publishes a huge amount of information, particularly with respects to US geology.
State geological surveys are great places for local geology and topographic maps. Different states have different policies about what they make freely available.
Searches documents from all science-related agencies in the US government. A great place to look for governmental reports or research if you're not sure which agencies might be involved.
The BLM deals with mining and national parks, among other things. There's not a lot of information here, but they do have some federal land records and legislation that deals with public lands.
Looking for images? The USGS photographic library has many images that are public domain, that means you're free to use them as long as you credit the photographer and the USGS.