The USGS is amazing. They have incredibly detailed information for the US: elevation (within 10 ft in many places), demographics, geology, and others. They have an amazing geologic map for Big Bend National Park [1] (a very geologically interesting park in southern Texas). Global maps are a lot harder to come by, unfortunately, although I did find a similar geologic map of the Earth as the one for Mars (divided by pieces) at [2].
The USGS really is great. It's one part of my government that I'm very proud of.
Here's a file I found a while back. Not Mars related, but pretty amazing. The national file is a delimited txt file with just about every geographical point of interest in the U.S. I've imported it into a SQL database and now run queries against it when I'm looking for a weekend road trip.
It's "NationalFile_20140601.zip - Download all national features in one .zip file "
I can't think of a way to query wikipedia - not like this allows. Once this file has been imported into sql (I use SQL Server), I run queries like
SELECT DISTINCT [feature_type] FROM dbo.nationalFile WHERE [state] = 'California'
This will give me a list of all types of features in California. From there, I'll see something that looks interesting (like "lava field" or "mine") and I'll run another query like
SELECT [feature_name], [latitude], [longitude] FROM dbo.nationalFile WHERE [state] = 'California' AND feature_type='lava field'.
This will give me a very clear list list. I can't imagine there would be a way to do this with Wikipedia, or any other online source that doesn't offer an API.
[1] http://pubs.usgs.gov/sim/3142/
[2] http://energy.usgs.gov/OilGas/AssessmentsData/WorldPetroleum...