Peak Z is sequenced with Peak X. One way mileage and elevation gain from Peak X will add an additional 1.4 miles and 1,250 feet of gain. On the return trip, you'll also have to gain between 400 and 500 feet elevation to get back over "Usable Pass." RT mileage and elevation gain from the lower campsite will be 7.7 miles and 4,475 feet of elevation gain. In this terrain, that's a serious enough day as it is.
The connecting ridge over to Peak Z looks pretty rugged, by way of Peak Y, so we ruled that option out, partly in the interest of time and partly because we didn’t want to find ourselves cliffed-out. Head back along the SSW ridge of Peak X to where you can start down the East ridge The ridge from the summit appears to be fairly difficult, but a better view of the east ridge prompted us to stop and reconsider. After some more study, we decided to attempt this east ridge, even though we had no information regarding it. For several hundred feet you can descend with relative ease, even though it is fairly steep. There was a drop further down where we could not see for sure what would happen, but thought we could manage it. So down we went.
As we descended this unknown ridge, the more we went down, the steeper it became. When we came to the section that appeared from above to drop off some, we left the ridge and began descending off to the right on steep tundra slopes with some rock. At times, it was so steep that we found ourselves gingerly crab-walking down short sections. Below us we could see that the ridge intersected a large couloir/trough that led directly south down to the more level, valley terrain. We headed over to the head of this couloir and then began descending it. There was some nice scree that allowed us to plunge-step our way down rapidly for a while, but it gave way to more rocks until things began to level out at about 12,000 feet. We were relieved to have successfully negotiated this descent without any overly difficult problems. Once out of the couloir, we turned eastward, walking over more gentle, tundra terrain now, interspersed with rock outcrops and flowers. We hiked past a beautifully colored shelf lake just above 11,880 feet with a few small trees around it. Once past the lake, we began ascending toward Peak Z.
Most of the lower ascent section is over tundra, with some boulder fields thrown in. Instead of going for the saddle/low point between Peaks X and Z, we decided to head right of the connecting ridge toward a steep slope that appeared to have some tundra, at least lower down, and that climbed up through a steep, rocky outcrop that guarded the flat south ridge of the peak. This flat area is very distinguishable on Peak Z from afar. The ascent through here is steeper than you might anticipate and we found ourselves using a cliff wall section for handholds as we ascended. Further up, we had to work our way through boulders and steep scree and then finally broke through to the flat southeast ridge. At this point, you are little more than 200 feet below the summit to the north. The remainder of the hike is easier, but still involves a little scrambling around boulders, etc. Looking back at the ridge between Peaks X and Z, we were glad we had not attempted a traverse. It was a very rocky ridge and had at least one section that dropped vertically. It most likely would have become a minimum of 4th class scrambling or even some 5th class work. Perhaps there's a report on it somewhere.
It took us about five hours to arrive at the Peak Z summit from the lower Pitkin Creek campsite and Peak X. Across the Boulder Creek drainage to the south, you are able to view Keller Mountain. To the north, there's a great view of Peak L, one the most difficult summits above 13,000 feet in this range. To return, descend back to the flat ridge area and if looking for some variety, take the southwest ridge back to the saddle and then turn south toward the bench area above 11,800 ft. You can follow that bench back to Useable Pass. We should have taken that SW ridge to begin with. Hiking down it was easy compared to how we went up and it was no problem hiking down to the bench level. A short distance beyond the shelf lake at 11,880 ft., the real fun begins. Following the bench southwest past the lake, we came to what we had avoided earlier in the day – a field of boulders that stretched a good 2/3 mile, all the way back to the base of Useable Pass. By descending the east ridge of Peak X, we had avoided almost all of this (and that was another motive for taking that descent), but now it's time to pay the piper.
Make your way west slowly and tediously, across the boulders of all shapes and sizes. Now a quick jaunt across a boulder field can be somewhat entertaining, but 2/3 mile is just plain pain in the rear, especially towards the end of the day. It seemed to take forever to get across and to the base of Useable Pass, (12,380 ft.) but we finally arrived there and then made the 300 foot ascent back up. The last 100 feet are difficult as anticipated, but we made it without injury and then began the hike back down the Pitkin drainage to our campsite. Return either to your campsite or the trailhead. If you manage to do this entire hike in a day, you are to be congratulated.
Links to other information, routes & trip reports for this peak that may be helpful.