• Dale Hill

GPS on Bench Marks - April 2021

Citizen Science and Crowdsourcing

There are 488 different Federally Crowdsourced Citizen Science Projects listed in the catalog on the Citizen Science website, all of the listed projects have been validated by federal employees. If you're looking for something cool to do, I'd definitely check out the catalog (click linked text above) and see if something strikes your fancy! Below is the description of the GPS on Bench Marks Program from the Catalog.


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.

My First Full Month in the Program


Just learning about this program in late March, I decided to hit the ground running with it. Working outward from home, I started marking my map with marks that needed to be located and verified, quite a few of these actually qualified as Drive-By Recoveries as they just happened to be located along roads I frequently travel either running errands or going to hikes. My initial plan was to include them in my monthly Drive-By Recovery post, but I decided it may be better to keep them separate so it's easier for me to manage the recoveries I make. Below I've created a hyperlinked table of contents that will take you to a particular mark, however, each has a story and it may be best to just read through in the order that I found them.


Jump to a Mark...

  1. DX0297: A 532 1956 (Ramona, CA)

  2. DC1358: A 1312 1978 (Poway, CA)

  3. DC0538: CY 77 SD CO 1969 (Julian, CA)

  4. DX0246: SY 119 1970 (Santa Ysabel, CA)

  5. DX5300: HPGN-CA SDGPS-15 1990 (Julian, CA)

  6. DC1128: PITCH 1955, (Poway, CA)

  7. DX0177: L 308 1935 (Julian, CA)

  8. DC1360: L 1312 1978 (Julian, CA)

  9. DC0550: CY 69 SD CO1969 (Julian, CA)


April 2, 2021 - SR 78, Ramona, CA


DX0297: A 532 1956 (10 km, Priority B-1 Observation)


Officially, this is my third GPS on BM recovery! The last four reported recoveries of this mark simply noted "Recovered in Good Condition" and did not include any additional information. The position information in the datasheet was "SCALED" which means it was calculated from a map as opposed to actual observations. My GPS reading had it located approximately 150 feet NW of the scaled location.

Finding this mark was a good example of why just plugging the coordinates into your GPS or Phone and setting out to find the mark can be frustrating, and often results in 'missing the mark'. If there is a datasheet available for a mark, you definitely want to print it out, study it, and bring it with you. I knew I was looking for a rock outcropping of a certain size based on the description information in the datasheet, when I initially arrived at the specified coordinates and looked around, there were no boulders or rock outcroppings fitting the description. I walked up and down along the shoulder looking for rocks that were fit the description, there was one, through some brush and dead limbs, under a large Oak tree. Some lower branches on the tree had recently been trimmed and the rock was cleared off, I walked around looking for the mark but didn't see it. I headed back to the truck to re-read the description, clearly, the rock I was on was the only one in the area that fit the description. One key descriptor was that the mark was 8.0 feet NE of the NE side of a 3-foot high granite boulder, I came back with my Bosch Laser Distance Measure and found the spot 8' from the boulder. Looking down, there was a slight depression in the rock filled with dirt, I kicked around it with my foot and uncovered some orange surveyors paint on the rock, BINGO! Using my small brush, I removed all the dirt and brushed off the disc to prep it for liquid chalk and pictures.


Standing directly over the mark, w/forward facing camera

As I was clearing the dirt off the mark, the landowners walked up and wondered if I was looking for the mark. They had uncovered it when they were clearing the rock outcropping. They had trimmed back the trees and removed over a foot of leaves, broken limbs, and debris from the top of the rock and are planning to put a picnic table on the rock under the tree. 😊 They had done an internet search and learned that the disc was a type of survey marker, but they didn't know much more beyond that. I explained the background and purpose of benchmarks and that this one was a priority for the NGS to verify its location as part of the GPS on BM initiative.


Unfortunately, while I made a good recovery and have updated location information, it won't be useful as a Passive GPS Location due to the tree completely obscuring the rock from above. I took my required "eye-level" photograph for my report, then, just flipped the camera to selfie mode and snapped this picture of the tree directly above the mark. Still, that's the type of information the NGS wants to collect with this project so this was a successful recovery.

April 3, 2021 - Poway Road, Poway, CA


DC1358: A 1312 1978 (10 km, Priority B-2 Observation)


Another Priority Recovery for the GPS on BM program AND I am the first person to report a recovery for this mark since it was monumented in 1978! According to the NGS Data Explorer, there have been 14 registered survey markers placed along Poway Road between SR 67 and the traffic signal at the intersection of Espola Road, the section that is locally referred to as "Poway Grade". Five of those marks are Vertical Control Marks (VCM) such as this one, the others are Benchmarks labeled as "Approx. Height" and include County survey marks as well as those marked US Coast & Geodetic Survey and National Geodetic Survey.

Recovering marks on Poway Grade is dangerous, there's no other way to describe it. I used to ride my bike up the Grade but switched to riding up Scripps Poway Parkway because Poway Grade has minimal, to no shoulder (you can see that in the first picture above) and the traffic moves at a minimum of 55 mph. There are turn-out areas where it's safe to park off the road, but that means walking along the roadway to look for the marks. The shelf where this mark is mounted was completely covered with dirt and rocks that had come from the hill above so the mark was totally hidden from view (I should have taken a picture beforehand, but wasn't 100 percent sure this was the correct location) I didn't have my trowel with me so I grabbed a flat rock and used it to clear the debris away, it was almost like chipping through plaster! When I saw the edge of the disc, I knew I'd found my mark! With the traffic whizzing past me just a few feet away, I flattened myself against the rock and continued to clear the area and prep the disc for photos.


April 4, 2021 - SR 79, Julian, CA


DC0538: CY 77 SD CO 1969 (10 km, Priority B-2 Observation)


This was a mark that I was unable to find back in February while recovering marks on a stretch of SR 79 that runs between Lake Cuyamaca and North Peak. When I learned that it was a Priority Mark in the GPS on Bench Mark program, and I was headed back to Cuyamaca Peak today to look for marks I hadn't previously found there anyway, I figured why not give this one another try?


New Power Pole Number for Reference

I revisited the coordinates I had saved before and made a closer inspection of all the rock outcroppings that were close in size to the one listed in the datasheet on the off chance I simply overlooked the mark before. Nothing.


The datasheet narrative included references to numbered power poles, so I headed back to the roadside to check pole numbers. None of the numbers were even close as all of these poles had been replaced (and apparently renumbered). I headed back into the field from the last power pole I had checked, pacing off the required distance, and decided to parallel the road looking for other landmarks called out in the datasheet as I went.


Success! I found the mark in perfect condition about 500-feet NE of its scaled location. One of the major landmarks referenced in the datasheet, a "twin-trunk 36-inch pine", was not so so lucky, it was just a heap of dead and burned wood.


I made note of the new number of the power pole and updated coordinates to include in my recovery notes when I upload this one to the NGS.


April 8, 2021 - SR 78, Santa Ysabel, CA


DX0246: SY 119 1970 (10 km, Priority B-1 Observation)


This morning I decided to make a quick trip out to Santa Ysabel and Julian to recover two marks listed on the GPS On Bench Marks list and I ended up also adding a couple of Drive-By recoveries along the way. Both of the marks I found today could technically be considered Drive-By Recoveries due to the proximity to the road but while they have assigned Permanent IDs and are in the NGS database, they are not noted on the Topo Map with any special symbol. This mark was an easy find right along the fence line off of NB SR 79 heading down into Santa Ysabel, the witness post made this a quick recovery.

April 8, 2021 - SR 79, Julian, CA


DX5300: HPGN-CA SDGPS-15 1990 (10 km, Priority B-1 Observation)


This was another easy recovery as it also had two witness stakes nearby. The first image is exactly how I found this mark, it's slightly below grade in a well made by 6" PVC pipe, the cap was laying off to the side. Interesting that this is mounted in a covered pipe when it's supposed to be used for GPS readings! If the cap is on, I don't imagine it would be "seen" by the satellites. This station listed two nearby reference marks, however, I was unable to locate either.


Providing a little Trail Magic.


While I was prepping the mark for my pictures, a couple of hikers approached me asking directions and distance to the Sunrise Trailhead for the PCT. I had been out there last month to recover the GAR Triangulation Sation, so I called up my track from that day and checked the distance to the TH, it was 9 miles. In talking to these guys, they were thru-hiking the PCT and had to take a Zero Day in Julian to take care of some personal business, now they were going back to resume where they left off. I told them to hang on for a few minutes while I wrapped up this recovery, and I'd give them a ride to the trailhead. Needless to say, they were very appreciative of the ride!


April 9, 2021 - Old Pomerado Road, Poway, CA


DC1128: PITCH 1955 - Elevation 467 Feet (10 km, Priority B-2 Observation)


This was my first GPSonBM recovery that was a named station, that doesn't necessarily mean it's more (or less) important than the others, it's just cool. Sometimes it's easy to figure out why a mark is named what it is, but I have no clue on this one. I'd actually had my eye on this mark as a potential Drive-By Recovery for a while because on the Topo Map its symbol appears to be right along my route to Costco. Once I realized it was part of the GPSonBM program, I decided to stop and look for it on my next trip to the store. Since this was mounted in a bridge abutment, it was pretty easy to locate.

April 11, 2021 - SR 79, Julian, CA


DX0177: L 308 1935 - Elevation 4,667 Feet (2 km, Priority B-2 Observation)


The funny thing about this mark is that it's literally just a few feet off the shoulder of SR 79 right at the intersection of Sunrise Highway (S2), you can pull off on the shoulder and easily see the mark set in the rock WITHOUT the pink fluorescent paint and big yellow "USBM" letters painted on the rock 😂 But what can you do, some surveyor just wanted to make sure everyone knew where the mark was!

DC1360: L 1312 1978 - Elevation 4,647 Feet (2 km, Priority B-2 Observation)


This was the second Vertical Control Mark in the "1312" line that I recovered this month (the first one was 'A 1312' in Poway, listed above). This one is located on the grounds of the Lake Cuyamaca Recreation and Park District that is a separate entity within the boundary of the Cuyamaca Rancho State Park. I already have an annual pass for this park, so I didn't have to worry about the $10 day-use fee to enter the park. The coordinates and directions to find this mark listed on the datasheet were way off! When I started my search using the original directions, it took me behind the restaurant near a maintenance shed and there were no rock outcrops near that area that fit the description in the datasheet. A park employee approached me to find out what I was doing (he thought I was some kind of inspector based on my clipboard of notes, and he was a little nervous about me poking around behind the buildings) He had no idea about the location of a survey disc so he flagged down another employee who had worked there for years. After repeating my pitch about what I was doing, this gentleman knew exactly where the disc was and pointed me in the right direction.


It turned out that the actual location of the disc was 0.2 miles SSE of the location described in the datasheet. The rock with the mark is located on the Park property inside a barbed-wire fence, while the witness sign (facing the road) is on the opposite side of the fence. The witness sign is easy to access by just pulling onto the shoulder off SR 79, but in order to get to the mark, you have to use the parking lot on the Park property. When I submitted this mark to the NGS, I included updated directions to find the mark, hopefully, they'll update the datasheet with that information.


DC0550: CY 69 SD CO, Elevation 4,315 Feet (2 km, Priority B-2 Observation)


This was a tricky recovery, located on a rock ledge along the inside curve of SR 79 as it winds through Cuyamaca Rancho State Park the mark was above my line of sight when I was standing below it on the shoulder (or what there is of a shoulder!) You can see from the first picture that there's no real shoulder to speak of and the ground drops off about 8 inches when you step off the pavement. Thankfully, this was the only significant rock face in the vicinity of the listed coordinates, and it took me a bit of climbing around before I finally saw the mark.



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