You can begin this ascent by hiking along the east shore to near the north end and then ascending through some willows and stands of wildflowers following a dry course northeast to a level area with grass, boulders and small tarns at about 11,900 ft. From here, keep hiking in a more northerly direction and access the green slope that leads all the way to the saddle high up on the East-West Partner Ridge. This will bring you out just east of the 12,620 ft. marker on the survey map. You can also circle around the west side of the lake and head up the main stream drainage north, then follow it NE to intersect basically the same route. The goal is simply to utilize the open slope of mostly tundra, scree and some rock to gain the ridge past (east of) the middle difficulties. From this point on, it's easiest to use our own original written account to describe the remaining route.
The information we had gathered indicated there would be a cairned route along the ridge to the summit of East Partner. So we began hiking along the ridge and the tundra almost immediately gave way to rugged blocks of rock. The first hundred yards or so is fairly easy with some scrambling mixed in. Then you will reach a section of the ridge where the contours tighten up at about 12,800 ft. It becomes quite clear at this point that further progress will require use of both hands. Continue along the ridge working mostly on the south side. We saw only a few cairns and these seemed to lead us below the ridge crest and even downward. A view of the remaining ridge will open up and the summit will be farther away than you might expect.
Continuing from there, things only become more difficult. The vaguely cairned route had led us a good 100 feet below the ridge crest and brought us to a place where we could see multiple rock ribs blocking our path and no clear way over them and no cairns to boot. So here, we decided to get back up to the ridge crest, since we had not seen a cairn in a while. This involved scrambling up a narrow, tight gully. The climbing became exposed and at least 4th class but we made it back to the ridge. Now we decided to stay as much as possible on the ridge, but several remaining obstacles continued to drive us off at times. We recall getting on the north side at least once and a few other difficult 4th class type moves or brief sections. This was all very time consuming, but finally, about three hours from our start, we made it to the small, rocky summit. That was a relief!
The Descent: For us, there was no difficulty in deciding that returning by the same route was not desirable. The route we had followed was so convoluted, we would never be able to retrace it. So we studied the prominent south ridge and it too, appeared to throw up many difficulties, so we fell prey to the enticement of the northeast ridge, thinking that we could surely find an easy way down into the east fork of Pitkin Creek. Descending along the ridge, we easily worked our way down to a saddle at the head of a broad couloir filled mostly with rock that descended southeast off the peak. This looked fairly enticing so we began descending it. At first, it was just a typical, rubble-filled gully of moderate steepness, but as we went down further, it began to constrict and get steeper. We had to negotiate some sections very carefully. Loose rock abounded and there were at least two places where we had to gingerly lower ourselves over rock walls in the center of the now narrow gully (3rd class). Along the way, we encountered some nice flowers. Well below us, we could see the valley floor and kept hoping that the intensity would lesson, but it never really became any easier until the last couple of hundred feet. Once out of the gully, we continued down on a talus slope that became more tundra covered the farther down we went. We turned more south in order to intersect the creek and did so with great relief. This had been a difficult and time-consuming descent. It was now approaching noon and we still needed to cover about a mile and a half to get back to the campsite and this would involve rounding the south ridge of East Partner and crossing from the one drainage to the other through uncharted territory. Having the opportunity to hike down this east drainage though had an advantage if returning this way for "Usable Pass" to access Peaks X and Z.
As we progressed down the drainage, we picked up a faint path through the lush growth of grass and flowers. The further down we went, the more evident the path, which lower down stayed well above the creek and always on the east side. (Not as we've drawn it on the map.) There were no cairns to follow but the path was still easy to observe and stay on. It was evidently not just a game trail. At about the 11,000 foot level, we found an easy crossing of the creek and headed across and into forest. (Be careful to cross back over to the west side of the creek before it drops into a more narrow sand entrenched section.) We descended on the other side a little more into a clearing and then began working our way westward to intersect the trail to Pitkin Lake. We only had to maneuver through the forest for a few hundred yards to locate the trail. At one point, we had to do a steep upclimb and then we found ourselves dropping into a narrow meadow area that the trail winds through. Once back on the trail, we just hiked back to our campsite. This complete circuit took us seven hours.
For those interested in doing the entire Partner traverse between the two summits, be sure and follow the two links provided for additional, useful reading
Links to other information, routes & trip reports for this peak that may be helpful.