He Devil She Devil Peak Survey

He Devil She Devil Peak Survey

Sept 16, 2023

Summary of Results: She Devil is true summit, 3.1 in taller than He Devil.

She Devil 9385.89ft +/-0.098ft, He Devil 9385.63ft +/-0.098ft (NGVD29 datum, same as quad uses, 95% confidence interval errors)

He Devil and She Devil are two 9000ft peaks in Western Idaho near the Oregon and Washington borders. They are well known because whichever is higher is an ultraprominent peak, with over 5,000ft of prominence, but until now it was not known for sure which is higher. They are almost exactly the same height. There are 57 “Ultras” in the contiguous United States, and until now this was likely the only one whose true summit location was not known with certainty. Whichever peak He Devil or She Devil is higher, even by an inch, is the true summit of the massif and is the Ultra. The shorter of the two is then not an Ultra.

The peaks were not directly surveyed on the quad, and both are within the 9400ft contour. Lidar coverage does not exist for the peaks (source https://www.idaholidar.org/existing-lidar-data/). Even if it did, Lidar errors might be too high to definitively determine the highest of the two peaks.

Several measurements have been taken to try to settle the controversy. In 2016 Greg Slayden surveyed both peaks with a 5x sight level and they were the same height within the error bounds of the sight level (this would mean they are within 6.4 ft of height for a 10-arminute resoultion on a sight level at the horizontal distance of 2000ft). In August 2023 Richard Hensley took elevation measurements of each peak with a survey-grade differential GPS unit. He found they were within 2 inches of height, but with error bounds of 3 inches. Unfortunately the error bounds were too high to definitively conclude which was the higher peak. But the measurement did establish that they are within a few inches of the same height.

Based on this data it is unclear which peak is highest, and thus which is the Ultra. Most climbers just climb both to be sure. The peaks are 2000ft horizontal distance apart, separated by a 4th class direct ridge or a longer class 2/3 route.

I’ve been surveying peaks around the world and around Washington and have equipment that is theoretically capable of measuring the peaks accurately enough to settle the controversy. I have a survey-grade differential GPS unit that has routinely been getting measurements with absolute errors <0.04ft for one-hour measurements. If the height difference is 2 inches or more, this error would be small enough to definitivily determine the highpoint. I usually get smaller errors for longer measurements, so in theory a 2 hour or longer measurement should get even smaller error.

I also own a 20 arcsecond mechanical theodolite. At a distance of 2000ft this can resolve a 2 inch height difference. So that height difference between the peaks would be at the edge of its capability, but if the height difference were in fact a bit over 2 inches then I could likely measure that. I decided to bring all my equipment and get as many measurements as possible to hopefully settle the controversy.

Mike and Marc were interested in joining. They both have survey experience, which would be very valuable. And they could help haul the 50 pounds of survey equipment. Friday afternoon I started driving over. Marc drove down from Spokane and met me in Colfax. Then we truck-pooled down to the seven-devils campground by 9:30pm. It was kind of crowded but we found a spot near the unmarked trailhead. As far as I could tell there was no fee for camping there.

We started up the next morning at 6am, just before sunrise. There was a bit of a miscommunication so Marc and I started first and Mike caught up later. I carried the theodolite in the big pelican case while Marc carried the differential GPS gear, mini tripod, big tripod, and measuring rod. There’s no trailhead sign and it was a bit confusing finding the official trail in the twilight. We ended up following a trail to Seven Devils Lake before we realized our mistake. We then bushwhacked through mostly open woods a bit northwest and then picked up the correct trail.

We followed the trail to the pass between Mirror Lake and Sheep Lake, then decided to follow the climbers route south towards the Tower of Babel. We mostly stayed near the ridgecrest or slightly on the east side, following occasional cairns and class 2 terrain. At the final saddle before the Tower of Babel we dropped down onto the west face and descended to 8400ft. We then traversed on scree and climbed back up to the ridge at the Baal – Tower of Babel col. From there it was an easy scramble to the summit of Mt Baal, where we took a short break.

We continued along the ridge following occasional cairns and trails until reaching the She Devil summit around 9am. I’d heard there used to be a big cairn on top, but it was flattened when we got there. The highest point was an obvious boulder, which I verified with my sight level was higher than any other point. Our plan was to take three sets of measurements. First I would set up the dGPS on the summit for a 2 hour measurement. Then Marc would stand on He Devil with the measuring rod and I would mount the theodolite over the summit. I would level the scope to be horizontal and see where it hit the measuring rod. We would communicate over radio. The final measurement would be I would find the angular declination to the He Devil summit.

It is non-trivial to get between the peaks so Marc started over immediately. I put the antenna on the antenna rod and mounted it on the tripod so the tip of the rod exactly touched the summit. Then I started logging data. Meanwhile I heard a yelp in the distance and it was Mike coming up along the ridge. He soon arrived at She Devil. We took a bunch of pictures and admired the view for the full 2 hour measurement.

I let it run for 2 hours 6 minutes to be safe, then saved the data. I then mounted the theodolite over the summit, with the bottom of the tripod head exactly touching the top. This way the measurement would be as repeatable as possible. I used my laser rangefinder to measure the height of the scope above the summit. On He Devil I could also mount it so the bottom of the tripod head touched the summit.

I radioed to Marc, who had made it to He Devil. I had given him the 5x sight level and he stood on the highest boulder, which was on the NE summit as verified with the sight level. He Devil has two summits, a SW and NE summit. I also verified with the theodolite that the NE was higher, and this was consistent with what Richard Hensley reported with his 5x sight level.

I measured angular declination angles to the summit, then Marc held the measuring rod on the summit. I leveled the scope and noted where it hit the measuring rod. It was too far away to see the numbers, even with 30x magnification, but Marc moved his hand up and we coordinated over radio for him to stop when it hit the scope and he told me the number.

After the final measurement we packed up and started down. I was kind of slow measuring and it was 1:30pm before we got moving. We followed the same route Marc did, descending the 3rd class west ridge to the He-Devil-She-Devil col. It was tempting to scramble directly up from there to He Devil to save time, but I knew it was 4th class and might be sktechy with all the survey equipment.

So we descended down scree and talus north towards Sheep Lake. We stayed high and traversed around He Devil. There was a small snow patch we got water from, then we followed the trail up the NW ridge. By 3:30pm we reached the He Devil summit, where Marc was taking a nap. We decided it would take too much time for him to go back to She Devil with the measuring rod, so we would skip that measurement.

It was getting sort of tight with timing to get all measurements done before dark, so I started next with the theodolite measurement. That required visibility, while the GPS measurement did not. I mounted the theodolite on the summit exactly as before with the bottom of the tripod head touching the top. I then measured the angle looking across to She Devil.

I then removed the theodolite from the tripod. The mini tripod couldn’t mount directly on the summit, so we left the big tripod over the summit and mounted the antenna rod and mini tripod on that. As before, the tip of the antenna rod exactly touched the summit and I ensured the antenna rod was perfectly vertical using the built-in bubble level. I started logging data at 4:30pm.

We hung out for the next 2 hours admiring the view. A few hikers came up to the summit, and they were very interested in what we were doing. None of them were aware of the controversy of which summit was higher, and they hadn’t heard of Ultra prominent peaks, so I’m not sure they completely understood why we cared so much about this survey. But they were very appreciative we were doing it.

Finally after 2 hours 6 minutes I stopped logging data. We quickly packed up and headed down. The day had been almost completely a hurry-up-and-wait day. We were either rushing to get to summits as quickly as possible, or killing time on the summits waiting for measurements to end. We hurried down, hoping to beat sunset as much as possible. We made good time down to Sheep Lake, then hiked back up to the pass to the east. At the pass we finally needed headlamps, and we hiked back to the cars by 8:30pm.

Mike camped out at the trailhead another night while Marc and I drove back north. I dropped him off at Colfax then made it to the Dusty rest stop by 1am. I slept there that night, then continued on to survey Snoqualmie Mountain the next day.

Results of post-processing the differential GPS measurements using OPUS rapid-static:

She Devil: 9385.89 ft +/- 0.098ft

He Devil: 9385.63 ft +/- 0.098ft

This means She Devil is 0.256 ft +/- 0.196ft taller than He Devil (3.1 in +/-2.4 in). In the worst case error for each, She Devil is still taller than He Devil by 0.06ft (0.7 in). These are the 95% confidence interval errors. If we assume each set of measurements is a normal distribution, which is generally true, this means there is a 99.4% probability that She Devil is taller than He Devil. To get this number I performed a Student’s t-test with the given means and standard deviations assuming 250 samples taken for each peak. My dGPS actually logged around 7200 samples per peak (one per second for two hours) but OPUS down samples to one measurement every 30 seconds. I haven’t figured out yet how to force OPUS to use all the data, but I still log all the data in case I want to increase accuracy of the measurement in the future.

Thus I’m confident reporting this final result. This means She Devil is the Ultra Prominent peak and He Devil is not.

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