Take the North Fork Big Pine Creek Trail to the Palisade Glacier. The maintained trail ends at Sam Mack Meadow, but a good use trail on the other side of the creek takes you up and over towards Temple Crag, around the terminal morraine of the Palisade Glacier above. Once the trail heads up towards the glacier it peters out on granite slabs. Follow the cairns on solid rock up as far as possible until you must climb the loose rock of the morraine. Climb down to the glacier and traverse to the far right side below Thunderbolt Peak.
This route starts at the base of the East Couloir Route (as described by Secor), but heads up to the notch between the two summits of Thunderbolt Peak.
Cross the bergshrund where passable, and climb up the lower portion of the East Couloir to the left of center. Climb up on the left side as possible, on class 2-3 rock. Further progress following the couloir is eventually blocked by class 4 cliffs. The climb starts from this point directly up the rocks towards the summit.
Climb a chimney system up until progress is blocked about halfway by a large chockstone. Move right out of the chimney onto a short section of friction climbing (this is the crux). Above here the route gets easier. At the end of the pitch you should be at the base of a steep gully leading upwards, and can belay from here. The second pitch is really no more than class 3 and can be done without a rope if desired. The rock is very loose and sandy here.
This gulley ends at the end of this second (long) pitch at the notch between the north and south (higher) summits of Thunderbolt Peak.
We used only a set of odd-numbered nuts and some slings for this route. The first pitch is mostly solid but has some loose rock as well. Wear helmets! We climbed using our hiking boots and had a single 50m rope.
This route is rarely climbed, as it isn't one of the listed routes in the standard guidebooks (Secor or Roper). Interestingly, we found a short section of hemp rope (about 6 inches) in the sandy lower portion of the second pitch. It had completely fallen apart before we could return with it to the trailhead.