These are links to US government sites that deal with geology. The US government publishes a huge amount of information, particularly with respect 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 EPA has a ton of great information dealing with the environment, but it's a frustrating site to use. I generally start by using the search box on the front page, or going to the A-Z index linked from the upper right corner.
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.