The route for Castleabra begins where the Pearl Pass Road crosses Castle Creek. As mentioned before, if you have 4WD with good clearance, it's possible to drive all the way up into the basin below Castle Peak at just under 12,800 ft. Otherwise, strap on the hiking boots and walk up the Pearl Pass Road to the SW for 1.8 miles until you come to an intersection at the third of a series of switchbacks. For those who wish to drive no further, there is parking here for several vehicles. To continue, take the right fork that heads north into the Castle/Conundrum Basin and proceed all the way to the upper parking area just below 12,800 ft. That's another 2.25 miles.
From this upper parking area, there are two basic routes to the summit of Castle Peak. A trail has been built that goes up along the NE ridge and that is now considered the "standard" route rated at a Class 2. The other route climbs to the Castle/Conundrum saddle. If the snow in the basin has receded enough, the upper portion of this route, just below the saddle will offer a steep, loose dirt ascent to the saddle. For most of the summer, you can expect snow on either route. This is a good place to practice some ice axe technique. When we climbed Castleabra in 1993, we chose to take the route to the Castle/Conundrum saddle. The basin was so filled with snow that we did not have to contend with the loose gravel/dirt. Both routes rate a Class 2. Either route covers about one mile to the summit.
From the saddle, hike SSE to the summit of Castle with just a few rock-steps along the way, but generally the ridge becomes steeper the higher you go and with more loose rock. If you've already climbed Castle before, it's tempting to think you can contour over to the saddle on Castle's west ridge at 13,580 ft. The contour however, would be extremely tedious on very unstable rock, so we judged it as best to just go on over the summit of Castle. (If you need more detail regarding a climb of Castle, consult Gerry Roach's book on the 14ers.) From the summit, turn and head west down along the ridge that connects over to Castleabra. The initial descent from the summit of Castle will be on loose, small rock. The first ridge step can be easily handled. The second presented more of a problem to us. The north side of the ridge will appear to offer the best way through the step, however, in 1993, we found ourselves at the head of a large snowfield. The gap between snow and rock at the head of the snowfield provided a way to contour across the head and make our way back to the ridge but working between the snow and the rock was slow and difficult. When you reach the first saddle at 13,580 ft., this is where the most significant obstacle is to be found. There is a large gash that drops 60 vertical feet or more. We descended off the ridge on the north side utilizing ledges covered in loose rock and sand. Progress was slow and tedious because we had to be very careful. Rock fall is a problem so helmets are useful here. We made it into the gully below the gash/saddle and then climbed back up a good 100 vertical feet before beginning a contour on the north side of the 13,820 ft. ridge bump. Getting past this gash was where we encountered the 3rd class work.
The attempt to contour below the 13,820 ft. point was met with slow progress on more unstable, steep, broken rock. On our way back, we chose to just go over the top rather than contour again. The drop to the next saddle presents only minor obstacles with little to no delays. The remaining ridge to the Castleabra summit will become clearly visible now and consists of an easy walk-up on tundra, some rock and possibly snow. The summit will offer an great view looking down into the Conundrum Basin as well as the Cumberland. The Cumberland approach to Castleabra requires more hiking, but the climb is easier overall. You can read a good report on that approach on LoJ. From this summit, you have a view of all the Elk Mountain 14ers.
For the return trip go back across the connecting ridge as you came, repeating the 3rd class traverse down to and back up the to bypass the gash. As you approach the Castle summit, again it will be tempting to contour north and avoid going over the summit. You will likely find as we did that doing so will become very unappealing. We ended up contouring only about 200 feet below the Castle summit and that was tedious enough. Go back to the Castle/Conundrum saddle, then hopefully enjoy a rapid glissade back down into the upper basin. Return to wherever you left your trusty vehicle.
Links to other information, routes & trip reports for this peak that may be helpful.