I'm very late adding this report, but I'm getting ready for my hiking/climbing trips this year and realized I never added this trip. I did a 4 day trip to the west to hit King's Peak and Borah in Idaho, and King's was my first stop. I decided to drive to the Henry's Fork trailhead, camp there, and get an early start for a day hike. I was worried coming in... there were thunderstorms all over the Salt Lake and southern Wyoming region, but they thankfully stopped by the time I got to the trailhead. Be warned though: the county roads leading to the Henry's Fork trailhead are VERY bad when wet; I had a newer model Ford and had to say a prayer every time I came to an incline in the road. Coming out the next afternoon, they had already dried and I had no problems.
Grabbed an open campsite and hit the trail about 5:00 AM the next morning (after setting off my rental's car alarm, sorry to anyone who may have been in the campsite). Morning was chilly, started out in a long sleeve base layer with a Marmot 3-in-1 jacket plus light gloves and North Face low-rise Hedgehogs (waterproof, better agility on talus). Pack had first aid/sunscreen/whatnot, some food, a Patagonia R1 for an additional layer, extra socks, 3 gallon full bladder, and a Kataydin pump filter. THERE IS NO WAY YOU CAN DO THIS WHOLE HIKE WITH A STANDARD BLADDER, YOU MUST BRING A FILTER OR TABLETS. Was expecting another dreary day, but it ended up being gorgeous which created a problem since I didn't have a buff, so always stash something like that in your pack as well.
Initial portion of hike rises roughly 1,000 feet over about 5 miles, no steep hills, easy trail to follow. Fully under tree cover, and even with the rain I didn't encounter any crossings that were problematic. At 5 miles, you pop out into a meadow and that's basically it for the tree cover, so remember that when coming back because there's nowhere to hide from the sun or weather. Cross the river, go up again for a bit, and then a long 2+ mile hike through the upper meadows to Gunsight Pass. I encountered 3 different streams in this meadow, the last was maybe 1/2 mile before starting the Gunsight climb. I don't know if those streams are there in dry weather, so assume the last on-trail water is right when you enter this meadow as the trail heads away from the river at that point. If needed, though, there are cross trails at various points that lead to the numerous lakes that feed the river so you should never be in an outright water emergency in that area. Make sure to get situated with water before going up Gunsight because I saw no water between there and the summit that I would consider filtering, even in the wet weather.
When you get to the top of Gunsight (call it 9.5 miles in), you have a choice: the main trail goes right back down the other side of the pass, through a valley, and climbs back up after about a 2 mile right handed turn. The quicker way, and the way I chose, was to turn right at the very large cairn at the top of Gunsight and traverse across the hillface to gain the ridge directly. The trail for this portion is definitely there but it's somewhat faint... just start looking around to the right of the cairn and you'll eventually make it out. Note that when it takes you up to the top of the ridge, aim for the left side of the ridge even though it's further from the summit: if you go center or right, when you come over it you'll be in a talus field that the hikers in front of me aptly referred to as "fucking bullshit". Be prepared for brief Class 3 scrambling here as the trail doesn't switch up to the ridge, you have to climb straight up the final 50 feet or so.
Once on the ridge, you can see the summit in front of you and the trail coming through the meadow south to north, gaining Anderson Pass on your right. Head down to the trail and follow it up to Anderson. Once on the Anderson Pass ridge, you can see the summit about a mile away to your left (south), but over 1,000 feet higher. The trail pretty much disappears here and you have to make your way up through a giant pile of talus, so make sure you're comfortable with Class 2 and 3 scrambling. You'll lose sight of the main summit and hit several false peaks, just keep bearing to the right and you'll eventually get there, there were no hard areas although I did guess wrong a few times and had to reverse to find a passable scramble route. I'd recommend coming down the way you came up: I went straight down the talus field (east) back towards the meadow and that was very unstable and dangerous. I saved time but I could have easily gotten into a lot of trouble.
Made it back around 4 PM, after filtering 2 liters at the river. I think most people will want to treat in the high meadow streams or lakes. Again, even on a cloudy day, I can't see 3 liters being sufficient for this hike for anyone so pack a treatment option! Thanks for reading.