Its all good . . . the only places "off limits" are in the State Park.
118 is good everywhere you can find a hillside or a road cut, Musquiz, Observatory, and along Limpia Creek. Snakes also are out and about at cool temps here - I got an Observatory male last year at midnight with the temp around 60. In July of this year, I found lepidus active at the Observatory at 1:30 am (and another one sitting in feeding position at 2:00 am), temps again near 60.
The Observatory is almost entirely a cut-hunting affair (either afoot or by spotlighting). From about 10:30 - 11:00 downhill traffic can be annoying if there's a STAR Party at the Observatory. I know of only 1 alterna AOR here, but lots off the cut.
To the best of my knowledge, no alterna have been found in the canyons up beyond it on 118 - but I've seen leps, bairds, and blacktails up there. There's little traffic, too, but it cools off quickly and is fairly shaded. Its lower than the observatory, but less exposed - it usually starts cooler and stays that way.
Limpia canyon (17) probably offers the best bet for seeing an alterna on the road, but traffic (particularly on the weekend) can be really bad. I've only seen alterna there DOR, unfortunately. Hunting cuts on 17 is hazardous unless you walk - there is no shoulder to get off on if you try it from the car, so you have to be ready to punch it at the first sign of headlights in the rear-view mirror.
Scout is the driest place in the Davis . . . don't know what the rain has been like up there this year . . . its so far from the rest of the "good runs" that I don't usually go up there (also, the good section of the scout is only about 1 mile or less). Its definitely a good road, but it can also be a pain when there are parents picking up or dropping off their kids . . . also, if another hunter is there and doesn't cooperate by spacing with you, it can be a pain.
The cuts on 118 near the state park are not bad, either. I've seen 2 alterna, lots of lepidus, blacktails, blackhooded snakes, night snakes, and bairdi on those cuts.
I've actually found warmer temps up at the Observatory early in the evening when compared to 118 along Limpia or in Musquiz or 17 in Limpia Canyon . . . I think the rocks are still radiating heat until about 11 or so, while down along the creeks there is so much moisture and vegetation that evaporative cooling drops the temps more quickly. However, after 11:30, the temps even back out and the Observatory gets cooler.
That's my experience hunting the place 15-16 nights the past two years . . .
Troy