• Dale Hill

March 2021 'Drive-By' Survey Marks


While most of my recoveries are on hikes or specific outings where I'm looking for one or more specific markers, there are the ones that are just 'along the road'. I call these 'Drive-By' recoveries because I'm driving with my GAIA GPS USGS Topo map in 'follow' mode and I can see the benchmark notations along my route. It's mostly about keeping your eyes open and paying attention.


Many markers are located along active roadways, use common sense, take appropriate safety precautions, and exercise due care to avoid potential injury. If you choose to search for survey marks it is at your own risk. Please do not disturb or remove Survey Markers!


March 6, 2021 - SR 78, Ramona, CA


DX0275: D 62 1927 - Elevation 1,873 feet


This benchmark was located on the north side of SR 78, just above where a private driveway connects to the road, it is 3.97 miles from the intersection of Main Street and 10th Street. The intersection of Main and 10th, is sometimes considered the 'center' of town and is also the junction of SR 67 and SR 78.

This benchmark is mounted in a typical concrete monument and is a Vertical Control mark (as noted by the black circle on the National Geodetic Survey (NGS) Data Explorer map, see the image below). According to the NGS Blue Book:


A vertical control point is defined in this publication as a survey point which is described and monumented (or otherwise permanently marked) and whose elevation is to be determined in an adjustment (OBS data) or whose elevation is available from other sources. A vertical control point is commonly known as a "bench mark" (BM).

In my composite image, I grabbed screenshots from the NGS Datasheet, USGS Topo Map, and the NGS Data Explorer to show how these are all interconnected and working between multiple sources, can help you locate a mark. What I didn't include here was the descriptive data in the datasheet, but you can see the full DX0275 datasheet 👈🏻here.



March 14, 2021 - SR 79, Wynola, CA


I found these two Benchmarks along SR 79 as I was passing through Wynola on my way to Cuyamaca Rancho State Park to hike Middle Peak.


DX0228: Elevation 3,948 feet

This one is identified on the USGS Topo Map as BM 3939 and is on the SB side of SR 79 before you reach Pine Hills Road.

DX0234: Elevation 3,654 feet


This one is identified on the USGS Topo Map as BM 3655 and from the map, it appeared to be on a side road behind a business on SR 79. It is located on the east side of Orchard Lane, in the front yard of a private residence a few feet off the road.


March 25, 2021 - Ramona, CA


DX0293: E 301 1935 - Elevation 1,485 feet


I was headed over to Pamo Road to check out the trailhead for Saturday's Big Black Mountain hike, this mark was along the route at the intersection of Elm Street and West Haverford Road, it's noted on the topo map as BM 1484. This is a good example of a Benchmark that is set properly with the top of the disc pointing North.


US Forest Service Location Poster - 012S 001E, Sec 26, West ¼


This USFS Location Poster was an unexpected find along Pamo Road. Normally it's just a matter of seeing there the tack is hammered into the sign to determine what part of the section boundary it marks, however, this sign has seen better days and the bullet holes make finding the correct location a bit more challenging! I always take a photograph either directly over, or in front of a 'found' survey mark to capture its latitude and longitude, then I can map it in GAIA and give it a "√" icon as found.


Interestingly, this sign was in the same general area of BM 934, and from a distance, I thought the sign was the witness post for the Benchmark C 301. I searched the area for the Benchmark but was unable to locate it, when I checked the survey information when I got home, the mark was reported as destroyed in 1963.


San Diego County Surveyor Monument RA 66


As I was driving back out on Pamo Road I just happened to look across the road and I saw this monument right near the trail and knew right away it was some kind of survey marker. After a while of looking for these, I tend to recognize witness posts and concrete monuments where previously I wouldn't have given them a second thought.


When I got home I searched San Diego County's Online Survey Record System (SRS) for any survey conducted in this particular township. I found a County Topo Map that had been updated in 1992 that showed this marker (circled in red on the image below) The map was accompanied by four pages of Vertical Control data for this map quadrant, Jackpot!

March 26, 2021 - Ramona, CA


HPGN-AZ SDGPS-37


Browsing around the San Diego County SRS, I pulled up topo maps for the quadrangles adjacent to Ramona and saw a variety of different survey records, most of them required a fee to download, but I found I could view low-resolution copies through the online viewer. I noticed that there were several SDGPS sites nearby (I had found SDGPS-14 on Volcan Mountain earlier this month) so while I was out today running errands I thought I'd pick up a couple that appeared to be "easy" recoveries. The SDGPS-14 marker on Volcan was part of the California High Precision Geodetic Network (HPGN-CA). When I saw that SDGPS-37 (located along Highland Valley Road) was stamped as part of the Arizona HPGN, I HAD to collect it!


DX5302: 70-6 SDGPS-32 1991


Located off Rangeland Road, not too far away from SDGPS-37 as the crow flies, was SDGPS-32. This one was interesting for a couple of different reasons.


  1. It was the first SDGPS station that I found that WASN'T stamped as part of an HPGN network.

  2. It was the first SDGPS station that I found that had a Permanent ID in the National Geodetic Survey database.

  3. It was stamped with two dates, 1971 and 1991. According to the datasheet, this mark was monumented in 1991, so perhaps the surveyor that set it simply stamped "71" instead of "91" in the outer ring at the bottom of the disc.



Probably the coolest thing about this mark, however, is that it is on the National Geodetic Survey's priority list of marks that need to be verified as part of the GPS on Benchmarks Program (GPS on BM), Priority B-1 Observation Requested.

GPS on Bench Marks Initiative

In an effort to improve the National Spatial Reference System (NSRS) and prepare for the NSRS modernization in 2022, the NGS has called on the surveying community to participate in validating certain marks in the network. Additionally, they are strongly encouraging Geochachers to participate by completing a recovery form for marks they locate.


GPS on BM will always include three important steps: recover, observe, and report. Recovery is the official term for locating the mark. The 'observe' piece of the puzzle is taking the appropriate photographs, one close up, one from eye level, and one that includes the horizon, preferably facing South. To 'report' the recovery, the NGS has an online form to submit your recoveries and upload your photographs. Once validated and accepted, they will update the Recovery information on the datasheet, the photos will be accessible from a link in the datasheet, and the item will be removed from the priority list as "completed".


I've submitted recovery information before, usually just to provide photos to add to the datasheets. This program actually puts some value and meaning behind my hobbyist scavenger hunting! There are three other marks in Ramona that are on the list that I'll look for (all B-2 priority), but I am going to focus on those with an A-1 or A-2 priority. There are quite a few in San Diego County to look for, so I ought to keep busy without having to travel too far. As it turns out, one of my previous recoveries is on the A-1 Priority List, I just need to go back and make sure my photos meet the standard and then submit the recovery.


What will April Bring?


I am at the point where I really need to go back and catalog all my recovered marks for easy reference, sooner rather than later, I'm going to lose track of how many of each kind I've found!


March was a good month for locating survey marks on my hikes and, as shown in this post, while I've been out and about. I am continually blown away by all the different types of survey marks I've found, whether the style of the mark, the issuing agency, the particular markings, or the history behind it. I wonder what new recoveries I'll have in April?!

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