I'm doing this from memory, so I might be off.
From Yellow Jacket pass on HWY 13 ,there is a road that goes east that is the dividing line. South of that ATV'a are allowed. North of that, it is closed to ATV's. If you can get far enough up that road, hike into the back side ( north) of Sleepy Cat Peak and hunt that. Rough country,but productive
If I was hunting Unit 12 in 1st or 2nd season, that is where I would hunt. The road in to Sleepy Cat is fairly decent on the west side. To continue on the east you need an ATV or vehicle with really high clearance as the road quality degrades significantly. There is a road the comes up from the south past Lake Avery/Big Beaver Reservoir (depending on whether you look at a map or the state signs), This road can get pretty nasty and there are places you will want chains on all 4 if it is muddy.
If the snow is deep on the ground and the migration is on, the Sleepy cat area (and all the high country) can be pretty bleak. Last year I saw hundreds of elk low while the guys that spent the week up high saw nothing.
North of Sleepy Cat there is an access road that enters the forest on the NW corner. This will get you to some lower ground. There is also the Jensen State Wildlife Area just west of the forest which can be accessed off 13 north of Meeker or from a turnoff south of Yellow Jacket Pass. Jensen has lower ground with good hills and can be very productive. You will want chains if the road is muddy.