Elevation: 13106 Feet
Trailhead: South Lake, Bishop
Route: Southeast Slope
Technical Difficulty: Moderate Ski
Aspects: South, southeast
In June of 2019 we set out looking for good corn snow lingering in the Sierra's huge snowpack following the spectacular 2019 winter. We didn't want to hike too far to find good snow so we started at the high trailhead of South Lake in Bishop (9850 feet). We took the line of least resistance up Mt Gilbert which approaches via the Treasure Lake basin and summits Gilbert via its mellow southeast face. We found fantastic views of the evolution range and the palisades as well as excellent corn snow above 12000 ft and "good enough" snow below that to facilitate a speedy return to the trailhead.
It had been warm in Bishop so when we started out from South Lake we quickly encountered all the summer skiing hazards that the Sierra has to offer, including melted out trails, unstable snow bridges, and mashed potato snow. We began on the Bishop Pass trail that was dirt for the first mile or so before transitioning to snow. I could hear the sound of a snow-melt fat stream running loudly up ahead and I worried that we wouldn't be able to cross it safetly. Sure enough we came to a river feeding South Lake and began looking for a way to cross. I flailed around in brush for a while without any success. Greg returned from his scouting with a dour look on his face. He'd found a way but he said he didn't really like the looks of it. I followed him downstream...to a full on wooden bridge spanning the stream, at which point he broke into a huge grin.
As we passed treasure lakes we began to see a wall of dark rock overhanging the valley we were ascending. A steep-looking couloir cut though the wall. When we arrived at the chute, it was too steep to skin so we began putting in a boot track. I was feeling strong so I broke trail upwards though very strange snow. It wasn't frozen hard like the snow we'd encountered so far; rather it was soft throughout all the layers. I believe now we'd found a patch of isothermal snow, or snow that has lost its temperature gradient after many freeze/melt cycles. Unfortunately this type of snow is most vulnerable to wet-slide avalanches and if we'd been better informed we might have stopped here. But in the moment we didn't recognize the risk and continued to the top of the ridge. From here, the southeast face of Gilbert is readily visible and we continued up this to the broad flat summit.
After thoroughly enjoying the views, some of the best I've seen in the Sierra, we put on our skis and began the descent. The southeast face of Gilbert had formed perfect corn and we ripped though it back to the chute. The chute was difficult to ski due to the heaviness and wetness of the snow and I tumbled out of the mouth of the chute head over heels into the bowl below, landing in an undignified position below the rock band. Greg followed with better style and we continued with no further mishaps down good corn back to the trail.
Looking back on this trip, I wonder whether we put ourselves at risk skiing the isothermal snow in that couloir. From a risk-management perspective we had done a good job up to that point, starting early enough so that >95% of the snow we encountered was either frozen solid or good corn. But something about the topography of that couloir had allowed the formation of a warm, wet snowpack. Theoretically it could have slid on us especially during the descent and perhaps we should have turned back as soon as I recognized that there was something unusual about that location. I think we generally operate under the assumption that wet slides are less dangerous than slab avalanches, mostly because they kill fewer people
Route Description:
Angle climber's left around south lake, or skin across it if it's well frozen. There is also a summer trail here in low snow conditions. At the far end of the lake you will encounter a creek running steeply into south lake. Work your way up this, don't fall in. There are some helpfully placed bridges, hopefully you will encounter them. At the top of the creek you will reach Treasure Lakes. Two valleys rise steeply from here. Take the rightmost valley and aim for a notch in the ridgeline. This is a steep snow couloir (pictured above). We had to boot pack up this. Once you have gained the ridge, you can see Mt Gilbert rising to climber's right.
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