Snoqualmie Mtn Survey

Snoqualmie Mtn Survey

Sept 17, 2023

Eric and Anthony

Summary of Results: East/Harder summit is true summit, 3.0ft taller than West. East Summit 6281.4ft +/-0.1ft, West Summit 6278.4ft +/-0.2ft (NGVD29 datum).

Snoqualmie Mountain is a popular peak in the Snoqualmie Pass area. It has a steep climbers trail starting from the Alpental parking lot. I’d hiked this trail in 2017 and hadn’t been aware of any controversy about the true summit location. However, this summer Eli Boardman went up to the summit and later revived an old thread on nwhikers from 2009 (https://www.nwhikers.net/forums/viewtopic.php?t=7977153&highlight=boardman) about controversy surrounding the true summit location. This was later debated on the pnwpeakbaggers group, bringing it to my attention.

The issue is the trail goes to an easy summit on the west side of the peak, and this is where almost all hikers stop. This is widely considered the true summit. There is even a USGS survey marker on the rocks near the west summit. However, there is also rock spire 545ft to the east that many people have noted appears to be of similar height. The USGS quad confusingly puts a cross on the west summit with 6278 written over the east summit. “Snoqualmie” is written over the east summit and “Snoqualmie Mountain” next to the west summit. Based on the quad it is unclear where the true summit is or whether that was surveyed. Survey markers are generally put where it makes sense to mount a theodolite for measurements, which is not necessarily the highest point on a mountain. The USGS doesn’t necessarily always care which peak is the true highpoint.

The east summit spire can either be climbed by the direct west ridge, which is 5th class, or by spiraling around to the east ridge, which is exposed third class. Whichever of these two peaks is higher is the true summit of Snoqualmie Mountain.

As far as I’ve read there have been five measurements of which peak is higher, but the results were inconclusive. In 2009 Sean Sullivan balanced a camera on the west summit and took a picture of the east summit. He used photo analysis software from Edward Earl using known peaks in the background of the picture to determine the hard summit was 2.3ft taller (+/-1.0ft error). This used two reference points in the background. Ideally many more reference points are used to increase confidence in this method. In my experience using this photo analysis method it is often very accurate, but sometimes can be off if there aren’t many background points. I would always want to verify it with ground measurements to be certain.

Yana on nwhikers said they used a clinometer on a compass in the mid 2000s and concluded the easy west summit was higher.

The summitpost article on Snoqualmie Mountain states the easy west summit is 6ft taller, but not details are given how this was determined.

Seattlehikertoo on nwhikers says they’ve climbed the peak three times and measured the easy summit 9 or 10 ft taller. They didn’t specify the measuring device or methods.

In July 2023 Eli Boardman analyzed Lidar data for both peaks and found the hard/east summit is 0.3ft taller than the easy/west summit. As a rule of thumb, I’ve been told by civil engineers to just trust Lidary to the nearest foot. The stated error in flat terrain for Lidar is up to 0.4ft. But samples are taken at 3-6ft horizontal spacing. This can easily miss a sharp summit, so errors can be even higher there. Both summits of Snoqualmie Mtn are sharp, so a 0.3ft difference from Lidar is within the error bounds of Lidar.

To compound add the error, there is a set of small trees near the easy summit that stick up several feet higher than the highest rock. It’s possible the Lidar measurement was measuring these trees. But that is not known with certainty.

I concluded from all this data that it was inconclusive which peak was the true highpoint. Luckily, though, I have the tools to accurately measure which is the true highpoint and settle the debate. I’ve been doing a lot of ground surveys around Washington this summer to determine an updated list of the true WA Top 100 peaks (my final results are here: https://www.countryhighpoints.com/washington-top-100-peaks-updated-list/). In early September I got back from Uzbekistan, where I conducted the first ground survey and first ascent of Alpomish (4668m, IV, 7-pitch 5.8), which I determined is in fact the true highpoint of Uzbekistan (link to detailed report https://www.countryhighpoints.com/alpomish-uzbekistan-highpoint/).

For my surveys I have a mechanical theodolite, a differential GPS unit, and multiple sight levels. With this equipment I can get absolute and relative height measurements with less than 1 inch errors.

This past weekend my main objective was to survey He Devil and She Devil peaks in Idaho. These are two summits of an ultraprominent 9000ft+ peak and it’s unclear summit which is highest. I would do that survey Saturday then drive home Sunday. But the drive home wouldn’t take all day, and I would likely have a half day to do another hike. I would already be driving back through Snoqualmie Pass and I would already have all my survey equipment with me. So it made sense to stop at Snoqualmie Mountain along the way and take a few measurements there to help settle the controversy.

It’s a lot of gear to haul up there (about 50 pounds) and one type of measurement requires two people. Luckily Anthony was able to join. He’s a surveyor for the army so his expertise would be very helpful. I’m just a mechanical engineer who taught myself surveying for fun.

Sunday afternoon we met up at 1:30pm at the Alpental lot. It was still very crowded, but I think most people were leaving for the day by then. I took up the theodolite in its big pelican case and Anthony took up the differential GPS unit, big tripod, mini tripod, and measuring rod. We hiked up the very steep trail as a handful of hikers were descending.

After about two hours we reached the easy summit where the trail ends. There is a big boulder that is the obvious highpoint, and there’s a patch of trees and bushes nearby that are stick up a few feet taller. My plan was to first take measurements with my sight levels. Those are the quickest and easiest measurements to take, though not as accurate as the theodolite and dGPS. The tree branches were obscuring the view to the east summit, but I had extra bungy cords from strapping the gear down, so I pulled and bungied the branches out of the way (no branches were harmed).

With both my 1x and 5x 10-arcminute sight levels I measured the harder east summit clearly taller. After noting the exact angles measured and doing some rough trigonometry assuming a 500ft horizontal distance I found it was at least 3ft taller. That was kind of a relief that it wasn’t just 0.3ft taller as Lidar said. That would be a tougher measurement to be confident in. The Lidar must have been picking up the cluster of trees and bushes that stood up a few feet taller than the easy summit.

I still wanted to get as many measurements as possible, though. I never want to trust a single piece of equipment since it could potentially get bumped on the hike and mis calibrated somehow. But if I get multiple independent measurements from different pieces of equipment and they all agree then I am confident publishing the results.

I next set up the theodolite exactly over the summit. This was a bit tricky but the legs extend and we made it work. I leveled the theodolite with the dials then I used my laser rangefinder to measure the height of the scope above the summit. I pointed the cross hairs at the east summit then measured the angles on the C and D dials. I then flipped and rotated the device to account for errors in leveling, and repeated the measurements. The final angular measurement would be the average of the four.

The scope was 25.1 inches above the easy summit and I was still looking up above horizontal to the harder summit. So even before processing the results I knew the theodolite was reading the harder summit over 2ft taller than the easy summit.

The next measurement we planned to do was Anthony would scramble to the hard summit and hold up the measuring stick. I would then level the scope and see how high it hit. However, this requires that the cross hairs on the scope hit above the opposing summit. We extended the tripod legs as much as possible to get the scope as high as possible, but when leveled it still hit below the hard summit. So this method wouldn’t work. The height difference was too much.

Ideally I’d then bring the theodolite over to the hard summit and measure angles back to the easy summit. But it looked to dangerous to haul it up to the tiny exposed summit spire, so we skipped that measurement.

Next, I would take the two sight levels and the dGPS over to the hard summit. I’d measure angles back to the easy summit first. Then I’d try to mount the dGPS on the hard summit to get an absolute height measurement. We intentionally did this one last.

For the absolute height measurement the longer I let the unit collect data the more accurate the measurement. If I want 2 inch accuracy I can usually get that from a 30min measurement. The minimum measurement that is accepted if I use the OPUS online processing software from USGS is 20 minutes, so to be safe I’ll usually get at least 30 minutes. If I want errors less than 0.7in I might take a 2 hour measurement, which is what I did for He Devil and She Devil peaks. But, since three previous measurements all showed the height difference of at least 3 ft we decided the 2 inch accuracy would be sufficient. Also, if I just took 30 minute measurements on each summit that would take us to about sunset anyways.

I packed up the gear and headed over. I first thought maybe I could scramble the direct west ridge. I followed a faint trail to the ridge and started scrambling over. It soon got very exposed, and I reached a 5th class downclimb that I didn’t want to do. So I retreated. I then remembered the beta that the back side ridge was just exposed 3rd class. So I backtracked off the cliff, then hiked down steep heather and rock slopes on the south side of the summit block. I traversed east at the base of the cliff, then scrambled up a 3rd class gully to gain the east ridge.

From there I followed the ridgecrest as it go narrower. It was indeed exposed 3rd class. Just below the summit was a small flat area where I ditched my pack. I took out the two sight levels and made the last few exposed moves to the small summit. I whipped out the sight levels, but then realized I couldn’t actually see the easy summit. The trees obscured it too much from that distance, even with the branches bungied out of the way.

I yelled over to Anthony to stand on the top. He could have held the measuring rod, but with only 5x magnification there was no way I could read the numbers. (The theodolite has 30x magnification and can just barely read the numbers at 500ft distance I’ve found). The best I could do was set the sights to 0 degrees and note down where they hit Anthony. It was between his knee and waist. So this at least confirmed the easy summit was a few feet shorter, though I wouldn’t report that to the nearest inch for that measurement.

I then returned to my pack and got out the differential GPS unit. This is a Spectra Promark 220 with Ashtech antenna. I’m borrowing the unit from Seattle University where I teach Mechanical Engineering and Civil Engineering courses.

I have a special mini tripod for the device just for situations like this. The summit is a slanted rock about 3ft wide with cliffs on the sides. The exact summit is a corner, so I couldn’t mount the tripod there. I wriggled over the top onto a ledge on the west side just below the summit. I played around with the tripod for 10 minutes and finally found an orientation that seemed sort of stable. This had the bottom of the antenna rod touching a point 3.5 inches below the summit, which I verified with my tape measure. I noted that in my field notebook and I would then add 3.5 inches to the final measurement after I post processed.

I mounted the antenna on the tripod, screwed in the connector cable, and fired up the main unit to start the measurement. It was pretty precarious with me balanced on the ledge and the tripod balanced at the edge of the cliffs. I was happy to be taking the shortest measurement. I held onto the cable just in case a puff of wind were to knock the tripod over.This was definitely the most precarious measurement I’ve ever taken.

Finally the 30 minute timer finished and I saved the data. I took down the tripod and gingerly scrambled back down. I retraced my route back to the easy summit, where Anthony had been patiently waiting. We just had one more measurement to do, and that was the dGPS on the easy summit.

The summit boulder has a vertical face meaning the mini tripod wouldn’t fit exactly. But we removed the theodolite from the big tripod and mounted that tripod exactly over the summit. Then I put the mini tripod inside the big one so the antenna rod touched the exact summit and was perfectly vertical. I then started logging data.

We admired the amazing sunset and chatted with one other hiker who came to the top. Interestingly he had heard of my Solitude Peak survey a few months earlier, where I discovered Solitude Peak is in fact on the WA Top 100 list.

The 30 minute clock finished and we quickly packed up just as the sunset colors were getting good. We hung out a little more to enjoy the view, then headed down in the dark. Our round trip time definitely wasn’t a speed record, but we were able to barely squeeze in all the measurements.

After waiting 24 hours for all base stations to report results I was able to post process the dGPS data using OPUS, then convert to NGVD29 datum (same as used on quad) using NCAT. I found the East/Hard summit is 6281.4ft +/-0.1ft and the West/Easy summit is 6278.4ft +/-0.2ft. This means the East/Hard summit is the true summit, 3.0ft +/-0.3ft taller than the West/Easy summit. The sight level and theodolite measurements were consistent that the East/Hard summit is at least 3ft taller, so I’m comfortable reporting the results, given that six independent measurements all agree which peak is tallest. The dGPS has the smallest error, so those are the final results.

If you want to support gas money for future surveys you can click the button below. (I’m just doing these surveys for fun, not part of any job and not paid.)

 

 

© 2023, egilbert@alum.mit.edu. All rights reserved.