Sherman Peak Survey – Removed from WA Top 100 List

Sherman Peak Survey

July 5, 2023

Eric and Kahler

17 miles, 3am – 4:30pm

Summary of Results: Sherman Peak elevation 10,133.0ft +/-0.1ft (NGVD29 datum), prominence 395.4ft +/0.3ft, removed from WA Top 100 list since prominence <400ft

I’m continuing my project to determine the most accurate list of the true top 100 highest peaks in Washington, and next on the list to survey was Sherman Peak. In order for a peak to qualify as a top 100 highest peak it must have at least 400 ft of prominence. Prominence is a measure of how high the peak sticks up above the saddle connecting it to a higher peak. Requiring 400ft of prominence ensures minor bumps on a ridge are not counted as separate peaks. The peak must stick up enough on its own to qualify.

Sherman Peak is has very close to 400ft of prominence based on the USGS quad, and until now it has been assumed that it had either exactly 400ft of prominence or a little above that, so that it barely qualified for the list. However, the saddle between Sherman and Baker was not directly surveyed on the quad. It was just approximated by 40ft contours. This makes it one of the edge cases that I have been looking into.

There exists Lidar coverage of Sherman Peak and the saddle, but it is inconclusive. I opened the Lidar point cloud in QGIS and found this gave Sherman a prominence of 396ft, which would mean it gets kicked off the list. However, when I open the DEM (digital elevation model) of the same data from 3DEPDEM, it shows a prominence of 405ft.

The point cloud and DEM agree on the summit elevation but disagree on the location and elevation of the saddle between Baker and Sherman. This is referred to as the key col, and determines the prominence. It appeared based on the point cloud and some pictures I’d seen of the saddle that there was an interesting sharp rocky feature in the area of the discrepancy.

Scramblin Rover from nwhikers noted that if eliminate the “uncategorized” points in the point cloud and only include the points categorized as “rock”, this removed the interesting rocky feature. This could potentially be what the DEM was doing.

This seemed like a plausible explanation, but not quite definitive. The Lidar point cloud had a published error of up to 4 inches, but it can be closer to a foot or two in weird terrain where the points are spaced far enough to not sample all features. Because the Lidar prominence was within a few feet of the 400ft threshold and it appeared there was an interesting rock feature near the critical key col, I felt a ground survey was necessary to eliminate any uncertainty in the prominence.

I could in theory bring my theodolite to the saddle and point it at the summit, then use the measured angle and the distance determined from Lidar to determine the prominence. But there was no guarantee I could actually sight the summit from the saddle without either an intermediate feature blocking my view or the summit being rounded enough that I couldn’t see the true top.

Luckily I had just acquired another tool that would be perfect for the job – a survey-grade differential GPS unit. This is capable of 1 inch vertical accuracy if a one hour measurement is taken. It has access to many more satellites than a standard handheld GPS unit, has an antenna that can correct for multipath errors, and collects enough data to allow for corrections for atmospheric distortions based on nearby base stations.

I had just tested the unit a few days earlier in the north cascades, and had measured the prominence of Solitude Peak. I determined that Solitude had just enough prominence to count as a WA top 100 peak. So I planned to use that unit again on Sherman Peak.

Kahler was interested in joining, and he had actually previously been on a surveying expedition with me in west Africa. On that trip we had used a similar unit rented from Compass Data to discover/survey the true country highpoints of Togo, Guinea, Ghana, Benin, Guinea-Bissau, Gambia, Senegal, and Ivory Coast.

This time, though, I had cut the weight down and had a small 1ft-tall mini tripod.

Tuesday night we met up at the Shreibers Meadow trailhead on the south side of Baker. It had cleared out after the long holiday weekend, and we hoped there would be a nice boot track to follow up. We planned to take the Easton Route since I’d heard the Coleman-Deming had a road closure 5 miles before the trailhead. I usually take the Squak route when I ski Baker, but that was less likely to have a good boot track. We weren’t skiing this time, so Easton it was.

Wednesday morning we were up and moving by 3am. Some years people are still snowmobiling here in early July, but this year everything was very melted out. We made fast time up the trail, crossing the one stream on a nice board just upstream of the trail. We then followed the railroad grade as the sun started to come up.

We passed a few tents around 5500ft, then reached the end of the rocks and stopped to rope up. I led the way and we had an excellent boot track to follow. We soon passed a group of six climbers and continued up. I think I set a fast pace but I was feeling good and knew we’d get a full hour rest at the saddle waiting for measurements.

By 8am we reached the saddle area and dropped our packs. The first order of business was determining the exact location of the saddle. There was indeed an interesting rock feature with sharp fins sticking up and even slightly overhanging in places. Maybe this is why the Lidar data was weird.

There were two candidates for the saddle, one where the climbers trail went and the other on the other side of the rock feature. I carefully scrambled to the east saddle while Kahler stood on the west. I whipped out my sight level and measured that my eye was level with the tip of Kahler’s outstretched hand. We then used the tape measure to measure the height to my eye and the height to his hand and subtracted to find the height difference.

We found the east saddle was 20 inches higher than the west saddle. This was accurate to about +/- 1 inch. This meant the west saddle was definitely the true saddle since it was the lowest point on the ridge connecting Sherman to Baker.

I then set up the differential GPS unit exactly on the true saddle and started taking measurements. Meanwhile, I noticed I could actually see what appeared to be the summit of Sherman from the saddle. I took out my 5x and 1x sight levels and measured angular inclinations up to the summit. This likely wouldn’t be accurate enough to be definitive, but could help build confidence in the results from the differential GPS.

The sight levels measure angles to with 10 minute accuracy, though there are also errors with aligning the bubble and pointing at the exact summit. Since the summit of Sherman is a bit rounded when looking from the saddle I expected to have a slight underestimate of the angle and thus a slight underestimate of the prominence.

As we were waiting and taking pictures the group of six came up. They were very interested in our results and I promised to text them when I had processed them in a few days. One of the climbers had a funny comment to the others, “Ok guys we can turn around now – the scientists just measured that this is the true summit here.” (They continued up to the summit of Baker, of course).

After the hour was up I saved the data and packed up. We then headed towards Sherman. I’d been to Sherman once before in November with Jake, and remembered traversing to the south face and climbing steep rime ice directly to the summit. I suspected the summer route might be slightly different, though. From the saddle the SW ridge looked nice and gradual. So we planned to gain that.

We dropped down, hiked around some steep rock features, and weaved around some crevasses. I then kicked steps up steeply to a weakness in the ridge. At the edge of the snow we ditched crampons and rope and climbed some choss to the ridge crest. Once on the ridge the terrain was very mellow. We easily hiked up until just below the summit.

There we found a steep dirt step that looked tricky to mantle up. I went around, using my whipped pick in the dirt and kicking steps up. We soon gained the ridge and were at the summit.

I set up the GPS unit and started logging data. I then took out my sight levels and was barely able to sight the saddle. It certainly helped that we had already been there so I knew exactly what to point at.

We hung out for the full hour, admiring the views of Baker to the north, shuksan and the pickets to the east, and glacier peak to the south. I soon logged the data, then packed up. This time to go down the steep step we each scooted across au cheval. I don’t often get the opportunity to do practice au cheval on dirt.

We made it back to the saddle by noon and still had plenty of daylight left, so decided to tag Baker as well. I had climbed it a bunch of times but this would be Kahler’s first time. We made good time up the boot track, and were soon on the summit.

I contemplated setting up the GPS to get another measurement, but the summit was large and flat, probably 7ftx12ft, and would certainly have a very accurate Lidar measurement. So I didn’t bother with the GPS.

We snapped some pictures and then headed back. By now the snow had softened nicely and we quickly plunge stepped back down the Roman wall and eventually back to the railroad grade. We took off the rope and crampons and made the hike back to the trailhead by 4:30pm, then back to Seattle that night.

After waiting for 24 hours for enough data to be taken by nearby base stations I uploaded the raw measurement files to OPUS (NOAA’s online tool for surveyors to process data like this). I found the summit of Sherman was 10,133ft +/-0.1ft and the prominence was 395.4ft +/-0.3ft. This means Sherman Peak does not have enough prominence to qualify as a WA top 100 peak and is removed from the list.

I also checked my sight level results, and these gave me a prominence of 380ft-395ft. This had higher error bounds but was consistent with the result that the prominence is less than 400ft. Thus I’m confident reporting the final result that Sherman Peak is removed from the WA top 100 list.

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