We've only done this one once and we did it as an ascent from Mirror Lake at low water — in January 2012 during the drought winter. There was some ice on the slabs, but little flow in the canyon. We used the description in RJ Secor, High Sierra: Peaks, Passes, and Trails. The main thing is to be smart about it, be flexible, be willing to turn back and try a different way, don't climb or rappel yourself into a situation you can't get out of, and otherwise be careful. The route you take will vary depending on whether you go at high or low water, whether you do this as a descent or an ascent.
We chose to ascend for a few reasons:
- We were doing it in winter and weren't sure it could be done or how much ice we would encounter. We knew that if we went up something, we could certainly rappel back down, but if we rappelled down, we might be unable to climb up and we would be stuck. So it gave us a fairly guaranteed bail option.
- We had someone willing to drive up and pick us up in the evening, but nobody who could drop us off in the wee hours of the morning, so we would have had to leave a car in Tuolumne and then go fetch it. If weather came in an closed the road, that could be May!
- We didn't know anyone who had done it as an ascent and hey, we're climbers not canyoneers. Going up is just more familiar.
The main reason to do it as a descent is that it's a lot less work of course. One thing that we discovered, though, is that when you do this as an ascent, there are two additional advantages that make us think the ascent is the way to go:
- The scenery gets better and better. The low end of the canyon is lots and lots of walking over river rock and when you're tired and you've had a full day out, people tell me this is boring, fatiguing and you just want it to end. When you are upward bound, it just gets more and more beautiful all the time and you're tired, but you're drawn along until close to the very end by the sheer beauty of it all.
- If you start at the bottom, it's easy to pick up the climber's trail to Mount Watkins. It's a pretty good trail that starts from the north end of the main footbridge. This trail would be exceedingly difficult to find in descent unless you know where to look for it, but compared to walking the creek bed and bushwhacking, it's a superhighway. So you cover this first "boring" part pretty quickly. By the time you get to Watkins and this climber trail runs out, you have only a short walk to the canyon proper and the fun stuff.
There is one big disadvantage to doing it as an ascent. There are a couple of short sections of canyon, but I think people might say the most interesting parts of the canyon, that you skip. In most cases, we were able to visit those parts of the canyon, but then had to backtrack to find a suitable way up and around an obstacle. In one case, we could have made it in August if it were hot out, but since it would have required a swim and it was January, this was not really an option. So we did end up climbing up and around about 100 meters of the most interesting part of the canyon.
Beyond that, you pretty much just follow the river. In the descent direction, there are rappel anchors at various points, though in many cases you can easily downclimb. In the ascent, as I mentioned, you need to keep your eyes out for easy and safe (i.e. not loose) ways up and around obstacles. These are overwhelmingly to your left (north) as you're going up and all the guides and accounts we read suggest left. In the biggest case, though, we climbed relatively steep slabs to the right (south). Nobody recommends this, but if you are comfortable with easy fifth class slabs, this is a good option. Whereas the north side of the canyon often has lots of debris, brush and loose stuff, these slabs on the flanks of Cloud's Rest are clean and easy going — provided you're comfortable on fairly steep slab (slightly steeper, I think, than the obligatory slabs by Pywiack Cascade).
In terms of route details, they are widely available. Again, Secor is a good guide and that's what we used, though it did sometimes take a bit of pondering to reverse the directions. The only reason we cared about Secor's directions, though, is that we wanted to know how we were doing on time. Given the short January days and cold January nights, we did not want to spend the night out (we had wamr clothes and a stove, but still, it sounded unpleasant). So mostly we were using the guidebook to get a sense of our progress and plot this on the map. I suppose if we had had a GPS and a map, we would have just needed the river to find our way. On the descent, though, I think it would be helpful to have the guidebook to help you find the rappel anchors, which are perhaps not always obvious.
Otherwise, the Summit Post writeup on the route is quite good and lays it out in the ascent. So for ascending, probably more useful than the Secor account that we had. One thing that might also be helpful would be to save a few of our photos to your phone or print out a page of them. I've put times on them for when you look at the large version. That would help you gauge progress too.
Be safe. Have fun. Do NOT go alone. Be ready to turn back!