These units are immediately north of Yellowstone Park, and a bit to the east and west. There are more than two. I think there are 4 or 5, although sometimes they don't open all of them to sheep hunting.
In general, they open around Sept 15, but the sheep population is small and they are so scattered at that time, over a huge, rough area, that it makes for a hard hunt, to say the least! I read somewhere that it took an average of 79 days of hunting to bag one ram.
In addition, I have heard that trophy quality is poor. The rams tend to have very tight curls. So you may shoot a full curl sheep, to find that its horns only measure 33" or so (if that matters to you). OTOH - I have seen some pictures of nice rams taken from there.
With regard to the terrain - the 2 easternmost units are in the Beartoooth Mtns. One good thing about this is that you can get on the Beartooth Pass Rd. (Rt. 212 which is mostly in Wyoming) which takes you right up on top of the plateau at about 11,000 ft. (be aware that this road sometimes closes for snowstorms, and is usually closed permanently for the winter by early October). Then hike or horseback north, into Montana, and set up camp. There will be less climbing doing it this way.
If you come in from the north, in Montana, you have to drive up either the E or W Rosebud Rivers, or the Stillwater, and the end of the road is way down in the valleyat 5000-6000 ft, elev. You would have to hike up.
Once the quota for each area is reached, hunting must stop. In some areas and some years, the quota is only one ram!
I live just 1 hour from these units, and my strategy is to forget about them, and keep trying for one of the drawing units.