Yesterday I found myself wondering if it would be possible to make a grand traverse of the commonwealth basin, starting at Kendall and going all the way to Snoqualmie. After an amusing romp up Kendall, Red mountain was next on the list.
Well, actually Point 5720 (the thing just north of the Kendall Katwalk) was next. Starting from the Kendall Katwalk, there is a reasonable slope just north along the trail that will take you to the top of this small hill, whence a ridge runs west towards Red mountain. Unfortuantely, the ridge isn't a very easy place to walk. One slope is steep and the other is worse, while the ridge itself is covered in dense trees. After maybe half a mile you'll come to a prominant notch in the ridge, perhaps 150-200 feet deep. Coming as I did, you now have to scramble down a loose, steep hillside to reach it. In retrospect it probably is better to traverse the talus underneath the ridgeline instead.
The fun really starts from this notch. The western edge of the notch is formed by a solid rock buttress. From the saddle itself you're looking at a full pitch of mid 5th class (I'd guess 5.8 or 5.9 but I don't really know). Hard enough I wasn't going to try it without a rope. Slightly lower, maybe 100 feet below the saddle, there is a line of weakness that passes a pair of small trees. Climbing up this, you can then traverse past the buttress. It's low fifth class, quite exposed, but at least the rock is solid. That changes soon enough. Once past this buttress you can regain the ridge via grassy slopes and continue west until you reach the first of two more steep steps. Here the rock turns the characteristic red color of the mountain and its quality goes downhill quickly, as do the numerous blocks you'll be pulling off. Your best bet is to stay on or as close as possible to the ridgecrest itself where things are slightly more solid. There's one particularly daunting looking section halfway up the last stretch but it's really not that bad. A few final meters of talus lead to the summit, with views in all directions. Luckily, you can descend the standard route (a bootpath down the SW face) and don't have to worry about retracing your steps.
All in all, I can't recommend this route to anyone and am including it here more as a warning to anyone else foolhardy enough to try it. The rock quality, at least after the first buttress, doesn't make it worth hauling gear, but it's damn scary without. If you want something to put gear in, I'd take a look at the cliffs on the south side of Point 5720 or maybe keep going to Thompson (?). If you just want an airy not scary romp, go do the north ridge of Kendall. And if you just really want to get to the summit of Red mountain, take the bootpath.
A thick head or preferably some actual gear. Rock shoes might even be handy, but since it's more likely that your foothold will fall off the mountain than your foot off the hold, these will only do you so much good.