Check this site out...
http://www.huntinggpsmaps.com/ They sell maps for your GPS that will show you EXACTLY where you are, with public and private land all mapped out for you. My brother and I found these maps indispensible while antelope hunting BLM land in Wyoming this past fall.
They're a bit pricey up front, but well worth it for the piece of mind they provide, and if you buy the download version you get free updates for life. (They've e-mailed me about a few updates since our September hunt already). Plus they have the units for each species mapped out, so you never have to worry about accidently wandering out of your unit if you're hunting close to the border.
Nothing is marked in Wyoming (which was very strange to an Easterner used to nothing but Posted signs everywhere), so if you want to do it 'by the book' and make sure you never inadvertantly cross onto private land this is the way to go!