I am trying to plan a single car isolation hike. I like to start early and get most or all of my exposure and vertical out of the way before it gets warm, so the Glen Boulder, Davis trail, then back via Isolation and Rocky Branch looks perfect. But, that leaves me with 3+ miles of rte. 16 midday when it's hot, which doesn't seem pleasant at all. There also seems to be mentions of bushwacks to save some mileage, and isolation trail being pretty washed out in spots...

http://4000footers.com/MAP%20isolation.pdf

shows a cross country skiing trail that runs parallel to 16. Is that usable for hiking? Any other tips? TIA.

Getting the vertical out of the way early is admirable but is there a reason why you want to go to 5200 feet for a 4000 foot peak? The trail you take gets you close to Boott Spur which is 1200 feet above the level of your final destination. Granted, the trail to get to Isolation via that path IS shorter (I think the mileage via Rocky Branch and Davis trails is 6.3 miles versus 4.6 miles going via Glen Boulder to Isolation to Davis) but you will be doing 1200 feet of extra vertical on the shorter route. It also puts you back out on Rt 16 three miles downslope of your car as opposed to doing an out and back to the same parking area rather than a loop. On the plus side, if bushwhacking is an option you can shave considerable amounts of distance off either hike by cutting through the woods directly east of Mount Isolation to make the route shorter. I have seen at least one trip report mentioning doing this although I did NOT do it myself when I took a trip to the top of Isolation via the Rocky Branch trail in December of 2015. I thought the Rocky Branch trail could have been better laid out (the trail actually WAS the stream in a few places) but I saw no evidence of Isolation Trail being washed out when I went. Aside from a couple of stream crossings I don't recall the trail even getting close enough to the waterway to get washed out. Considering the dry weather we have been having I doubt it's as wet as usual. Hopefully someone has more feedback on current trail status.

The Glen Boulder trail looks really awesome, but up and back via that has more exposure and a lot of vertical at the end. Up and back via Rocky Branch looks easier, but wetter and less views, so trying to split the difference.

It looks like it might actually be 4.1 miles between trailheads, with a fairly regular downhill from north to south. Maybe the best play is to bring my bicycle, park at Glen Boulder and coast down to Rocky Branch, and go the opposite route I had been considering...

I agree with your change in plans. I was going to mention doing that but I wasn't sure if you wanted to change the vertical towards the end of the climb. You might be able to bushwhack off the corner near the Boott Spur trail junction to avoid some of the vertical too.

I put my bike rack on, inflated my bike tires and made sure the bike was still working. But, since Cori (dog) multiplied my options, I became paralyzed by over-choice and just went with my original plan - park at Glen Ellis Falls; go up Glen Boulder and down Rocky Branch. The bushwack near Boott Spur was obvious, but I wasn't sure how much vegetation I would end up stepping on or how important it was up there. I remember Moosilauke had signs saying not to walk on the above treeline vegetation.

Glen Boulder trail was totally worth the extra mileage! Cori did not like the 3 road miles at 78 degrees, but we stopped a few times for some shade and for her to cool down in the water. Doing it again, I would park halfway between the trailheads or so. I like getting some full strides in after a long descent, but 3 miles was too many.