Sentinel Peak and Old Guard Peak Surveys

Sentinel Peak and Old Guard Peak Surveys

June 11-13, 2025

Results: Sentinel 8256.9 ft +/-0.1ft, Old Guard 8259.6 ft +/-0.1ft NAVD88

Sentinel and Old Guard are two peaks in the Cascades in the middle of the famous Ptarmigan Traverse route. They are very close to the same height, and whichever one is taller is on the WA Top 200 list, while the other is just a sub peak. Sentinal was directly surveyed on the quad, but Old Guard was not, so it was unclear based on the quad which was taller. The Beckey guidebook described them as nearly the same height. Recent Lidar measurements showed Sentinel a few feet taller, but that is within the error bounds of Lidar so it was unclear. I’m working on conducting ground surveys to determine the accurate WA Top 200 list, so I wanted to measure each with a differential GPS unit to get elevations down to the nearest inch and settle the tie.

Tim and I had to pivot from our original objective when the weather forecast changed at the last minute, so we switched to doing a loop hike hitting and surveying both peaks. We would hike up the South Fork Cascade trail to the peaks, then down Drop Creek. I’ve been on the Drop Creek route a few times climbing Formidable, and I remembered it being easy bushwhacking down to the south fork trail, then the trail was lightly maintained back to the road.

I recently saw on nwhikers that CP3 had just freshly cleared out the trail, which was amazing. This trail has an interesting history. As far as I’ve heard, it was first created in the 1960s as an emergency exit route for the Ptarmigan Traverse. It went from cascade river road up to the South Fork Cascade Glacier. That glacier has a few gauging stations at the outflow and a large USGS research station at the edge. It is one of the world benchmark glaciers, and has been studied since 1959. There’s a helipad up there and researchers generally access it by helicopter.

A fire wiped out the lower section of the trail in 2003 and it was basically abandoned after that. In 2018 when I descended Mt Formidable the trail was in tough shape but followable, and in 2023 it was greatly improved by good citizen hikers, though it still didn’t go all the way to the lake.

We started hiking up the trail at 2pm Wednesday and made good time to the edge of the cleared section just past High Log Creek around 3300ft. From there we bushwhacked through mostly open forest, then crossed a short slide alder patch around 4000ft approximately following the old trail location. We occasionally saw orange flagging and hints of the old trail, though they weren’t super helpful. We eventually reached Salix Creek, then picked up old cairns at the edge of treeline.

By 9pm we reached the edge of the South Cascade Lake and laid out our bivy sacks to sleep.

Thursday morning at 8am we hiked up past the research station, then dropped onto the South Fork Cascade Glacier and roped up. We hiked up to intersect the Ptarmigan Traverse route, then turned up to the west face of Sentinel Peak. There we dropped packs and climbed up snow, crossing a bergschrund with some 4th class scrambling on rocks in the middle.

After crossing the schrund we traversed left on the upper snowfield and reached the edge of a nice class 2/3 ledge. There was loose rock and dirt on top and it was a bit exposed, but not enough to warrant a rope. Later in the season if the snow melts out more it will become sketchier to gain this ledge.

We traversed across to the broad west face, then hiked up easy class 2/3 terrain to the summit by noon. I set up the DA2 on the summit and started the 30 minute timer. I usually like to take a one-hour measurement, but we didn’t want to spend quite that long up there, so I settled for 30 minutes. That usually gets me 0.1ft vertical accuracy above treeline, which is pretty good. We had considered descending the east side of Sentinel from there, since the Beckey guide says it’s class 3, but it looked a bit too exposed from that vantage point for our liking.

After signing in at the register we carefully downclimbed the route and plunge stepped down to our stashed overnight gear. We encountered other footprints then, which appeared to be from a group that had just done the ptarmigan traverse. I later learned it was my friend Anthony a day earlier. We spiraled around the north, then stashed our overnight gear and continued roped up on the Leconte Glacier. We hiked up through a whiteout to the Old-Guard – Sentinel col, then ditched crampons and made the 3rd class scramble to the summit by 3pm.

There was a neat wall of clouds hitting Dome and Sinister to the south and rolling over, and I got a nice timelapse. I took another 30 minute measurement on top, then we scrambled back down and hiked to our overnight gear. From there we loaded up and continued following Anthony’s tracks north past Le Conte Mountain and then down to Yang Yang lakes by 6pm.

We had considered tagging Spider Mountain on at the end of the day, but by then it was socked in with clouds and very windy even in the trees. We decided to take advantage of the small amount of shelter and hunker down there to get some shelter for the night. No place was perfectly sheltered, but we set our bivy sacks out in a grove of trees and had a good dinner of ramen noodles.

I didn’t get much sleep that night with the cold and wind in just my bivy sack, but at least there weren’t any bugs.

Friday morning the thick clouds had descended more and visibility was low. We hiked north along the Ptarmigan Traverse, ascending into a whiteout. At the col before Pika Peak we decided Spider Peak would have to wait for better weather, so we descended down Drop Creek. We down climbed a bit of steep snow, then plunge stepped to the top of the cliff band at 6200ft above a cirque. We found an easy scramble down on the skiers right side, then finally descended below the clouds.

We stayed on skiers left of drop creek and had an easy exit through open meadows with no slide alder all the way to the old growth forest. From there we walked through mostly-0pen forest back down to the trail and started our hike out. On the way out we met a good citizen hiking in to clear the trail even further, which was amazing.

We got back to the truck by 3pm and were soon heading home. After processing the data I found that Sentinel is 8,256.9 ft +/-0.1ft, Old Guard 8,259.6 ft +/-0.1ft NAVD88. This means Old Guard is 2.7ft taller than Sentinel, so Old Guard is the WA Top 200 peak and Sentinel is a sub peak. Interestingly, Lidar from peakbagger undermeasured Sentinel by 3.2 ft and undermeasured Old Guard by 2.0ft. In general I advise only trusting lidar-derived summit elevations from peakbagger to about +/- 3ft for a summit. You can get the accuracy better if you manually inspect the point cloud data, though that takes a bit of work and is still within about +/- 1ft. I’m currently working on a scientific journal article about this exact topic.

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