You can shoot on most federal land, (and state land here) unless it is close for some wierd reason.
You're best maps can be bought from the USGS
You can also get BLM maps at your BLM office and National Forest/Grass Land maps at your local forest service.
The maps you get localy are normaly 1:100,000 scale. You can get 1:24000 on line for about a dollar a sheet. These low scale maps are better for shooting (and hunting). Mainly because you can use them as a range finder.
Just get a 1:24000 protractor to go with your maps.
Best shooting on public land I've found are deserted gravel pits. (They should be located on the map).
There is one about 2 miles from my house that I can shoot 2000 yards or better. One thing I like about gravel pits is there is less vegitation meaning less chance of fires.