On the trail from South Lake, the split to Treasure Lakes is marked and we (Stephan Meier and I) followed this split trail all the way to the bigger of the Treasure Lakes. The trail peters off, but heading in the direction of the stream that drains into the lake (refer to Mt Thompson 7.5 min quad), a smaller use trail is visible that can be followed till that too ends in a boulder field.
Johnson was now on the right as we came to the final Treasure Lake which we skirted from the left by going alternately over snow and boulder fields and after coming to the top of the lake decided to forego the planned south east scree slope and went straight up Johnson by striking a more easterly route till the ridge line. It was class-2 and some class-3 boulder climbing and we soon topped out on the ridge. Here the ridge is very narrow and slopes off to the right in an impressive series of slabs. The true summit of Johnson is visible in the distance at the head of the ridge. It seemed that we were now on the class-3 north ridge. At this point dark clouds had begun to gather and it looked like rain. We even felt a few drops. Fearing thunder and lightening, we hurried. It is a great walk on the ridge with that drop-off to the right. We remained on the left when in doubt and making good progress reached the summit at 12.50 pm, four and half hours after starting from South Lake.
The clouds were getting worse, so we spent only 15 minutes at the summit and hurried down. Instead of going back the same way, we headed for the south east scree slope. It is a simple way to get down but quite less exciting. A short break for lunch, a lot more boulder hopping, a small snow descent (ice axe not needed) yet more boulder traversing and we were back at the top of the biggest Treasure Lake.
At about 4.40, we were back at the cars for an eight and half hour round trip time. The class-2 SE slope may be used to go up too and then minimal class-3 is encountered at the summit area, but the ridge we took was a lot more fun with it's airy third class. Ice axes were not needed and the snow that was encountered was compact easy to walk on. This peak offers great high Sierra climbing within a short distance from the trailhead and is certainly doable as an energetic day hike.