As a PP said. The Mile is open entirely.

Below Pathfinder also has quite a bit of open ground as well, since you have the Cardwell area there. Fremont Canyon is also mostly public I believe.

The Wyo GF site has some great resources on fishing access, both normal public, and walk-in public areas as well.

If you fish Cardwell (Below the bridge at Pathfinder) or the mile, you may want to bring along a handgun to take care of any rattlers. Not to common, but not rare either.