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  • Writer's pictureDale Hill

Tying Up Loose Ends

Updated: Jun 10, 2023

Recovery Date: February 6, 2022 Total Marks Recovered: 12

Confirmed Lost/Destroyed: 0

Not Found: 0

Discs Recovered: 10

Non-Disc Type Recovered: 2

Notes: My total recoveries today include six marks on Carrizo Mountain that are not listed in this report as they were not part of the "clean up" effort but were new recoveries. They will be detailed in the article: Carrizo Mountain on a Whim

My main goal on today's Survey Mark Scavenger Hunt (SMASH) was to go back and tie up some loose ends with previous recoveries. It's not uncommon for me to make a second attempt to find marks that I couldn't locate the first time or return to recover marks that were nearby previous recoveries that I just didn't know about.

Research and Preparation

When I plan a trip dedicated to recovering survey marks, I will usually start out with a list of 30-40 potential targets. Using various online search tools through the National Geodetic Survey (NGS), I can identify registered survey marks along a particular route, or in a specific area. Each of the tools I'll describe below is linked to the NGS datasheets that contain all the recorded information about registered survey marks. The information provided in the datasheets can be indispensable in locating marks quickly and efficiently.

NGS Datasheets

For a detailed guide that explains how a datasheet is formatted and how to read one, check out this PDF document: DSDATA.pdf. I highly recommend printing datasheets for the marks you're going to look for as they often contain very specific instructions on how to reach the survey mark. Here is a link to the datasheet for my first recovery today, SDPR 4 (PID: AF9878), I'll go into more detail about this recovery a little later.

In an effort to maintain updated records on more than 800,000 survey marks set around the country and its territories, the National Geodetic Survey encourages the public to submit the current mark recovery information, you can learn more about that on the Survey Mark Recovery page.

Mapping Tools

The primary tools I use are:

  • National Geodetic Survey Data Explorer. The NGS Data Explorer was the first map that I discovered to help locate survey marks and it's still my first stop when I'm researching current or potential recoveries. The database includes survey marks that have been assigned a Permanent Identifier (PID), the unique PIDs consist of two alpha and four numeric characters. Survey marks are identified by various icons or symbols on the map based on the type of Control they are, clicking on the symbol will open a small pop-up window that includes basic information about the mark and a hyperlink to the datasheet for that mark.

Screenshot of NGS Data Explore and PID: AF9878, SDPR 4

  • The Beta NGS Map. This is a newer map and I tend to use this one more when I am out and about as it is GPS enabled and will show me marks near my actual location, of course, it is limited to having an internet connection, so it always pays to have a printed datasheet if you're looking for a specific mark. One of the nice features of this map is that the pop-up windows with the basic details of a survey mark show the status of the last recovery, very helpful in the case where a mark was reported as "NOT FOUND". In the case of SDPR 4 shown in the screenshot below, the last recovery was "GOOD"

Screenshot of Beta NGS Map and PID: AF9878, SDPR 4

  • NGS Data Sheets by Quad. The NGS Data Sheet landing page has a lot of different search tools, one of which is to search for datasheets by the U.S. Geological Survey 7.5-minute Topographical Map Quadrangles (Quads). This returns a list of all the stations within that particular map Quad.

USGS 7.5-Minute Topographical Quadrangles for San Diego County

Again, referring to my first recovery today, SDPR 4 (PID: AF9878), I know that it's located in the Agua Caliente Springs Quad, so when I enter that in my search criteria, it returns a table that lists ALL the marks within that Quad, form this list I can highlight the individual datasheets I want to view.

Search Datasheets By Quad - Agua Caliente Springs

If I select multiple datasheets to print (Get Datasheets), they will all be included in one document instead of having to print them individually as I would have to with the other tools.

  • GPS on Bench Marks for the Transformation Tool. The NGS is updating the National Spatial Reference System through a crowd-sourced data collection program called GPS on BenchMarks (GPSonBM). Anyone can participate by searching for, finding, and reporting back about the condition of the marks on the list. Those with access to survey-grade GPS equipment can help further by collecting GPS data on these marks and sharing it with NGS. I began participating in this program in early 2020 and have submitted close to 150 survey mark recoveries. The program was initially supposed to end on December 31, 2021, however, they have extended it another year. When I started, the number of GPSonBM priorities in San Diego County was CRAZY! I haven't looked at the list in several months, I was surprised to see that most of the priorities in San Diego County have been completed! A handful of the remaining priorities are ones that I have recovered and reported, but since I don't have survey-grade GPS equipment, they can't use the location information I provided. 🤷🏻‍♂️ (But LOTS of my photos are making their way into the NGS database!) 😉

GPS on Bench Marks for the Transformation Tool Map

Reality Check

With all these great tools and my emphasis on preparation, you may wonder why I have to return, occasionally multiple times, to recover a survey mark. Compiling a list of any more than a dozen or so marks is time-consuming and in many cases, the marks are easy to locate and I don't need the printed datasheet with me. Too, having made almost 900 recoveries, I have learned what to look for and understand the preferred placement of markers.

I've touched on my process of transferring my targets as waypoints in the GAIA GPS app, but I'll recap it here with the key steps.

  1. Determine the primary location(s) I'll be searching, sometimes I may make one mark the center of my search and look for others that are nearby or on my route to that location.

  2. Use the map tools listed above to identify the specific target

  3. Open the datasheet

  4. Copy the marks designation, for example: (AF9878 DESIGNATION - SDPR 4) and position (32 57 13.31871(N) 116 17 27.94428(W))

  5. On my desktop version of GAIA, I'll enter the position (coordinates) of the mark into the search field, then drop a waypoint at that location.

  6. I edit the waypoint to name it the designation, change the icon to a star then save the waypoint.

  7. I copy the coordinates and paste them into Google Earth Web to view the general area where the mark is located, sometimes I can even see the mark using "street view". This step helps me plan where I can safely pull off the road, gives me an idea of fences and other obstacles that won't show up on a topo map.

  8. I repeat this process for all targets on my list.

With the waypoints loaded into GAIA, I use GAIA like you would any other GPS-based map tool. As I approach a waypoint, I begin to look for a place to pull over and start searching. GAIA also has a driving directions function where I can select a waypoint and a route opens in Apple maps with navigation directly to the location.

GAIA Desktop - Waypoints and Hiking Tracks

The screenshot above is from the GAIA desktop application, for survey mark recoveries I standardize the icons I use; Stars to indicate targets, the Checkbox for successful recoveries, the Circle with the Slash through it for "Not Found", and the Skull and Crossbones for "Destroyed". Other symbols are hiking track-related.

Time To Dig!

SDPR 4 ~ PID: AF9878

Survey mark SDPR 4 was one of 5 marks, on my list of 50, for October 24, 2021, that I was unable to locate. I dubbed that trip my "S2 SMASH" and I had a great day making 45 recoveries. The roadside of County Road S2, also known as The Great Southern Overland Stage Route, is dotted with a variety of survey marks and there are a lot of Public Land Survey System (PLSS) Section Corners that are conveniently close to the road. I spent the day slowly working my way south from Scissors Crossing, stopping at each waypoint on my map.

On that first trip in October, I easily found the witness stake for this mark, but I could not locate the 6" PVC pipe that I knew protected this mark. The last photo in the series above was my eye-level picture of where the mark should have been. You can probably tell from the picture that I was kicking around in the sand hoping that I'd hit the PVC pipe cap. I didn't have a shovel with me on that trip and only a short metal stake to use as a probe, so I flagged this one for a return visit when I had the proper tools to continue my search.

When I got home from that trip and was entering all my recoveries into my database, I double-checked the "to reach" description for the mark to get the details of exactly where it was, then I copied and pasted it into the notes section of the waypoint for future reference.

With my trusty compact shovel, I returned today to make the recovery. As you can see from the snippet of the datasheet, the mark was 3 feet NW of the witness post and a 2008 recovery confirmed that it was located in a 6" PVC pipe with a cap requiring a pipe wrench big enough to handle the 2" lug. Had I checked this information BEFORE heading out that day, I probably would have been better prepared and could have found it then.

As you can see from the pictures above, the mark was right where it was supposed to be, albeit about 8-10 inches below grade. Thankfully, this was soft sand and easy to clear out of the way. I did leave the cap exposed, but it won't take long before the normal winds blow most of that sand back into the hole.

With this recovery, I have now found SDPR 1 (Ocotillo) through SDPR 17 (Ranchita), spanning 7 different USGS Quads!

Confirming Another 1941 U.S. Army Corp of Engineers "Oops!"


Mistakes happen, and I've encountered a few while I've been out looking for survey marks, usually, they are just misspellings that occurred when the disc was stamped. Today's recovery of the station disc VALLE, and its related reference marks, solves a mystery that I encountered back in November last year when I recovered the GUARD station disc and one of its reference marks, erroneously set as VALLE RM 2. This reference mark was set in the described location for GUARD RM 2, so it appears as if they had the disc with the correct RM number stamped on it, just the wrong station name.

I was not able to locate GUARD RM 1, my best calculations placed it in a location that may at one time have been on level ground, but now appears to have eroded away or has been the victim of subsidence or a slide, not an uncommon occurrence on many of the low hills in the desert.


As the crow flies, these two peaks are 8.75 miles apart, VALLE being 130º SE of GUARD. Both hikes are short, easy trips accessible off of the S2. The walk to VALLE was a straight shot, round-trip across the desert floor totaling just over 3 miles with about 230 feet of total elevation gain, I didn't even bother to bring my poles or pack for this one, just my survey mark recovery kit and a water bottle for good measure.

All three recoveries for this station were easy to spot, the station disc was in a small rock cairn near the register can and both reference marks were mounted in concrete monuments rising about 8 inches above the ground. I hit the station disc first, prepping and documenting the recovery, signed the register, then headed over to the reference mark SE of the station, this was properly stamped as VALLE RM 1. Finishing up this recovery, I headed to the other reference mark to confirmed my suspicions, it was stamped GUARD [actually, "GUAD"] 😂 however it was RM 1, not RM 2 as I would have expected! 🤔 Perhaps the "to reach" descriptions of the GUARD reference marks were incorrect, it's hard to say for sure.

Ultimately, I will likely return to GUARD and do a more thorough search of the area for any signs of the other reference mark. If the one stamped VALLE RM 2 truly was supposed to be GUARD RM 1, then it opens up a wider search area for the true GUARD RM 2.

Reference marks are numbered starting from the Geodetic Azimuth of the station disc, True North, and then increase in sequence as you move in clockwise around the compass. So for example, if you locate RM 1 at 180º (south of the station disc), you can expect to find RM 2 somewhere between 181-360º and very likely between 270-360º as there is generally at least 90º separation between reference marks. Of course, the terrain and availability of an appropriate place to set the mark can impact this, but it's a good general rule of thumb to follow. Caveat: my experience shows that the US Army Corps of Engineers didn't always follow this protocol of placing reference marks!

Return For Reference Marks

SDGPS-22 ~ PID: DC2132

First Pass: October 24, 2021 Station Recovery

Somehow during my preparation for the S2 SMASH, I overlooked that there were two Reference marks for the SDGPS-22 station (PID: DC2132). So I made a mental note, the next time I was out that way, I'd return to locate the Reference Marks.

Cleaning up: Reference Mark Recovery Today.

Today was THAT day! 🤣 Both RM 1 and 2 were easily recovered in great condition!

Wrapping Up

Today was a satisfying day as I was able to bring closure to a handful of partial recoveries that I'd made earlier.

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