• Dale Hill

GPS on Bench Marks - May 2021

Citizen Science and Crowdsourcing

GPS on Bench Marks is the National Geodetic Survey's crowdsourcing approach to obtaining survey-grade GPS data on a prioritized list of marks where new data will provide the most benefit. Surveyors, engineers, and technicians that work for Federal and State government agencies, universities, professional societies, and private sector firms use their GPS equipment to take measurements on survey marks in the areas where they work and share them with NGS via our online tools. The public can also participate by finding the survey marks on the priority list and reporting back to NGS on their condition and suitability for GPS observations. This crowd-sourced data helps to improve the local accuracy of national scale models and tools that NGS builds to serve the Nation.


Jump to a Mark...

  1. AF9888: SY 12 (Ranchita, CA)

  2. AF9883: SDPR 12 (Borrego Springs, CA)

  3. DX0367: BOR 12 (Borrego Springs, CA)

  4. AF9882: SDPR 11 (Julian, CA)

  5. DX5301: SAN DIEGO GPS 16 (Julian, CA)


May 22, 2021 - Montezuma Valley Road, Ranchita, CA


AF9888: SY 12 (10 km, Priority A-1 Observation)


I had originally found this mark last November while driving back from my hike to Travelers Peak. It was just about the time I really started paying attention to survey marks other than the ones that were on the peaks I was hiking. This was probably my first true Drive-By Recovery. Since it's on a frequently traveled route, I wanted to go back and take the appropriate photos for submission to the NGS GPS on Bench Marks program. The pictures I took back in November didn't include specific shots from one or more of the cardinal compass points and I didn't know to use chalk to highlight the markings back then.


Of the 16 survey marks I have recovered and submitted to this program, this is the only one so far that was on the 10km A-1 priority list.


May 22, 2021 - Palm Canyon Drive, Borrego Springs, CA


AF9883: SDPR 12 (10 km, Priority B-1 Observation)


Today was a great day for recovering marks in the "SDPR" line, I found a total of six before heading over to hike the Hellhole Canyon Trail to WEBO. The first five marks I found in this series (SPDR 17 to SPDR 13) started near the top of Montezuma Grade and were spaced out pretty evenly between top and bottom, all were recovered in good condition and were part of my May 2021 Drive-By Survey Mark Recoveries. Since this one is on the GPS on Bench Marks priority list, it's included in this post instead of as a Drive-By. I carry an adjustable pipe wrench specifically to remove this style PVC threaded pipe cap, but when I arrived at the mark, someone had installed the cap upside down and managed to tighten it pretty well. The underside of the square nut on the top is a round indentation with a removable button, so really no place to get any real traction on the cap. I must've worked at it for 15 minutes, I'm still not sure how I managed to loosen it, but I did and was able to make the recovery. Oh, and yes, I put the top back on the correct way!


May 22, 2021 - Borrego Valley Road, Borrego Springs, CA


DX0367: BOR 12 (10 km, Priority B-1 Observation)


As I mentioned in my May Drive-By post, I had found three Zone 6 Traverse Station Marks, CL 1, BOR 11, and this one BOR 12. I had the approximate location of this one from the NGS datasheet, but I really didn't need it. The disc is located on the bank just a little off the shoulder and the witness stakes made it an easy find.



May 26, 2021 - Great Southern Overland Stage Rte., Julian, CA


AF9882: SDPR 11 (10 km, Priority B-1 Observation)


Today's trip back to the desert was specifically to hunt for survey marks, I was headed to Blair Valley to hike the low hills above the valley and scout out a few peaks to see what I could find. I was happy to see another mark in the SDPR line was along the way AND it was on my GPS on Bench Marks priority list! Win-Win! Again, if this hadn't been a GPSonBM priority, it most definitely would have been a cinch as a Drive-By. With this recovery, I now have seven consecutively numbered marks in the SDPR line. I particularly like the "eye-level" picture of this mark because it shows the Pacific Crest Trail (PCT) just on the other side of the fence, and Granite Mountain in the background.


May 26, 2021 - Great Southern Overland Stage Rte., Julian, CA


DX5301: SAN DIEGO GPS 16 (10 km, Priority B-1 Observation)


It was cool to start out my scavenger hunt in Blair Valley with another GPSonBM priority mark. The interesting story behind this particular mark is that it's only 55 feet SE from a Drive-By Recovery that I made in early December last year.


On December 3rd, I located the USACE disc stamped BM SP 2 2578.11 FT. based solely on seeing the map symbol for a benchmark on my Topo as I was returning from hiking to Diablo Benchmark. It was a true Drive-By in that I had not researched the area ahead of time, consequently, I had no idea there was another mark so close. Because the SP 2 disc was lower, I could not see the witness stake for this mark.


With the appropriate research done for this trip, it was an easy recovery and I quickly moved on up the hill to Mescal Peak.

What to expect in June


Since learning about the GPS on Bench Marks program, I have recovered and reported on 16 survey marks on the NGS Priority List. I selected marks that were close to home or qualified as Drive-Bys as I was on my way to other hikes. Starting in June I will be selecting one or two geographic regions and going out specifically just to find the priority marks in that area with the goal of adding at least 10 new GPS On Bench Marks recoveries each month. Depending on how my efforts go in June, I may increase my monthly target so I can reach a total of 100 GPSonBM submissions by the end of the calendar year, we'll see.

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