Hmmm, this might be a new favorite in the San Rafael Swell. Considering that the competition includes Little Wild Horse and Bell, and Ding and Dang, that's saying something.
According to Michael Kelsey's book, Crack Canyon can be done as a 25 km loop with Chute Canyon. It was a very windy day out in the open terrain, so I figured that connecting the bottoms of the two canyons would be an unpleasant sandblasting experience. I opted to just do Crack Canyon from the top. The trailhead (well-marked) is 4.2 miles on the Behind-The-Reef road.
With 4WD high clearance you could drive another 0.8 mile or so to some nice primitive camping areas; beyond this point vehicles are not allowed.
The canyon gradually tightens up. There are several sets of narrows, with accompanying dryfall and chokestone problems. The hardest one is about an hour from the trailhead; some people can get up and down past the chokestone but it was a little bit more than I wanted to tackle by myself. As I went back up-canyon into the sun to eat lunch, I noticed the bypass route!
Eventually the canyon starts to open up again as you get down onto the valley floor. I went as far as the first side wash, and hiked a quarter-mile or so up that way just to see what was there.
Here is the bypass route (from the top) for the hardest narrows section. Go back up-canyon, back up out of the narrows about 150 yards or so, the canyon opens up. The wash makes a sharp right turn (almost 90 degrees), at the outer apex of the corner there is an 8-foot wide crack system that goes up as high as you can see. Scramble up the rockfall at the bottom of the crack to get onto the first ledge on the right. There are a few cairns here, I didn't see them the first time past but once I realized I needed a bypass I was able to find them. Coming back up-canyon, the cairns for the bypass are very obvious.
This is a popular place; on a sunny (and windy!) afternoon in early May, I saw 7 other parties in here. According to Kelsey's book, ATVs can use Chute Canyon so it is not quite as idyllic a place; I'll save that one for another day.
GPS log and photos at EveryTrail.com