I sent an email to my friend's dad and this was his response. Hope it gives you a start, or an idea of what to expect. He actually drew an any elk tag for the same unit this year. Depending on my hunting schedule, I may go help scout for him, if I do I'll let you know what I see.
"Most people who hunt Yakima road hunt, which obviously handicaps you considerably. Will anyone be going with him to help drag one out of the canyons? Normally the big bucks would be hanging out on the slopes as you guessed, but it'll be rut so the biggest ones will be harassing the does. The benches are probably the best bets in the late morning and early afternoon as they'll need a little rest before the next nights frolic. 4wd is absolutely essential, even for the road hunters in the best areas. There are off road restrictions though so there could still be a considerable pack involved."
Sounds like you need to call and see what the post restrictions will be, if they would even know that far in advance. See if they can send you any topo or post road maps. All I remember was lots of really long ridges that ran down to the Columbia River. Very open on the tops (short sagey cover) and some cover in the steeper gullys between ridges.
Good Luck
Mike