• Dale Hill

Flood Plain SMASH

Updated: Nov 25, 2021

Recovery Dates: November 5-24, 2021

Total Marks Recovered: 33

Discs Recovered: 31

Non-Disc Type Recovered: 2 (1-Washer, 1-Pipe Cap)

GPS on Bench Marks Priorities: 0

The Spark that Ignites a SMASH

The idea for this Survey MArk Scavenger Hunt started out as many do, with a random Drive-By Recovery that sent me down a rabbit hole on the interwebs, researching the why's and wherefore's of the survey mark that I recovered.

In this case, the catalyst was recovering the mark SDRF 1, a San Diego County Surveyor 3¼" brass disc set in the sidewalk of a bridge on Riverford Road in Lakeside, California. The bridge crosses the San Diego River, which at this location and time of the year, was bone dry.

The mark is actually quite close to my office and I travel this road frequently. I was driving back to the office from lunch and happened to spot what appeared to be a brass disc survey mark mounted on the sidewalk as I crossed the bridge. I pulled over at the end of the bridge, grabbed my recovery kit, and made the short walk to check it out. Sure enough, it was a Survey Control Mark so I prepped it, took the requisite photos for my database, and returned to work, the entire recovery taking only a couple of minutes.

Record of Survey 22056

I've recovered several discs placed by the San Diego County Surveyor, but it was the first stamped "SDRF". When I got home, curious about the origins of the mark, I headed to the San Diego County Online Survey Record System to do some research. Having used this system extensively, it was pretty easy to zero in on the area and scan the few maps and documents that came up in my search. I quickly found Record of Survey (ROS) 22056 which included SDRF 1. Usually, I just view the documents online, take notes for the survey mark I am interested in, and go from there. However, this particular survey included a total of 23 marks with their locations so it was worth it to pay the $12 to purchase a copy of the survey rather than transcribe all that data.

The first page provides an overview of the survey including a vicinity map, legend, notes, procedures, and technical information about how the survey was conducted, it also has the required statements attesting to the work completed and recorded.

The second page is a scale diagram of the control network that was established. I've embellished it with some color to highlight the different series of discs that I found. The San Diego River Flood Plain Control Marks (SDRF) are in yellow, Los Coches Creek Flood Plain (LCCK) in red, and the Alpine Creek Flood Plain (ALPC) are in blue.

I also recovered two marks that were noted on the survey as "found monuments", San Diego GPS 19 (SDGPS) and MLP 10 are highlighted in green. In total, I found 22 of the 23 listed marks, with only one (LCCK 6) having been Lost/Destroyed.

The mark highlighted in pink on the map is still on my list to recover, and I may or may not go back after it 🤔. RCE 12725 is located a few inches below street level in M-10 Monument Well with a triangle-shaped cast iron cover that is a pain to remove if you don't have the right tool.

The mark is stamped with the license number of the Registered Civil Engineer who originally set the disc, but that is the only marking. Perhaps my OCD tendencies will kick in and the desire to recover ALL the marks on the list will drive me back to document this one, but for now, it'll just sit there as the lone mark on the list that I didn't get.

The final page of the survey provided detailed information about all the monuments, this was the key document I used to plot where all the marks were located. In addition to a text description and location of the mark, the notes also include the northing and easting coordinates for each mark. I used an online conversion tool to convert these to Latitude and Longitude then created waypoints in my GAIA GPS App.

Once I had all the marks plotted in my GAIA GPS, it was simply a matter of heading out to look for them, which I completed between November 5th and 24th. None of these marks required any off-road hiking to reach as they were all very close to the roadside, as you can see from the photos, many are located in sidewalks or culvert headwalls. A few that were mounted in rock outcroppings or boulders provided a little challenge to find the "right" rock, but all-in-all, these were easy recoveries.

Flood Plain Maps

The San Diego River Flood Plain encompasses the largest area of the three that were monumented during this survey followed by Los Coches Creek and Alpine Creek. It was difficult to get a good image of the entire flood plain area that would display well but I finally settled on images from two agencies, San Diego County and FEMA.

This image is from the San Diego County Graphic Information Source (GIS) system. I used the checkbox menu to fine-tune my map view by selecting the Ecology section with the Flood Plain subsection. I experimented with zoom levels to capture most of the three flood plain areas in one image, at this level of zoom, there's not a great deal of detail but it gives a general idea of where things are at. Flipping between this image and the map above where I color-coded the marks I recovered, you should be able to see the relationships.

Flood plain maps are actually created and maintained by the Federal Emergency Management Agency (FEMA), you can visit their Flood Map page for more information. I did pull an image of the Alpine Creek flood plain zone from the FEMA site and will provide that alongside the ROS 22056 Map area for Alpine for comparative purposes below, but for now...back to the survey marks 😉

San Diego River Flood Plain - SDRF (9 marks)

The gallery below shows the rest of the discs in the SDRF "family", I generally take two photographs of each mark, a close-up and one at eye level to give a sense of where the mark is.

I prep the marks by removing the sand, dirt, or debris from the area, then I apply a small amount of liquid chalk and spread it over the surface of the mark. It drys quickly then I wipe off the excess with a rag, and use a Magic Eraser sponge to buff the remaining chalk residue off the disc, this process highlights all the stamping on the disc and makes them much easier to identify.

Los Coches Creek Flood Plain - LCCK (7 marks)

As you can see in the map above, Los Coches Creek flood plain is the next in order of size and there were seven survey control marks placed that were stamped with LCCK. This particular grouping had an unexpected or "bonus" recovery and one destroyed item

Bonus Finds: MLP 26 and LCCS XP 1

I had two bonus recoveries while working on the survey marks for this project, the first, MLP 26 was located in the San Diego River area close enough to where I had SDRF 3 plotted, that when I approached it, I thought I had found SDRF 3! 🤣 This one wasn't listed on ROS 22056, but I was happy for the unexpected find (a short walk down the road led me to SDRF 3.) The second bonus recovery was in the Los Coches Creek area. I have the tendency to categorize recoveries like LCCS XP 1 as "Random Survey Marks" but the truth of it is that there really are no random marks, they are all placed intentionally and serve a purpose. Since I began purposefully looking for survey marks, I am more aware of ALL types of survey marks and witness stakes and I simply see them everywhere.

I have found two others like this one that has the "XP" stamping and I have traced them back to survey maps, but honestly, I didn't look too hard for this one, I just thought it was cool because it was so close to the LCCK 3 🤷🏻‍♂️

Lost/Destroyed: LCCK 6

For the purposes of recording marks in my personal database, I use the four primary condition descriptions from the National Geodetic Survey: Good, Poor, Not Found, and Destroyed.

  • Good is self-explanatory and means there is no evidence of tampering.

  • Poor means there is some type of damage present, this could be anything from a badly marred disc to the actual disc removed with just the stem visible.

  • Not Found is straightforward and means the mark's existence is doubtful, but there was no obvious proof that it was destroyed. The mark might be buried or the coordinates were not exact. Just because it wasn't found, doesn't mean it's not there.

  • Destroyed means there is irrefutable evidence of destruction, I take this to mean there are no physical remnants of the mark left behind (no stem) but you can definitely tell a mark was there at one time and has since been removed. I refer to these as "Lost/Destroyed". In my experience, this could be a drill hole where you can tell the mark was pried out, leftover concrete or epoxy that was used to secure a mark, or the remains of a concrete monument.

LCCK 6 fell into that Lost/Destroyed category, you can definitely tell there was a survey mark set in this culvert headwall but the damage to the surrounding concrete exposed the disc and the stem that was originally set there. I can only speculate, but my best guess is that it was the result of an accident, such as a vehicle or piece of heavy equipment clipping the edge of the headwall. I originally thought this was an act of vandalism, but I was able to find an image on Google Earth that shows the loose mark sitting on top of the headwall! Go Figure! 😲

Regardless of the "how", this mark has been destroyed and as such, I count it as a recovery in the destroyed category. Out of the 785 marks I've recovered as of writing this article, 35 have been in the destroyed category.

Alpine Creek Flood Plain - ALPC (4 marks)

The smallest of the three areas in this survey, Alpine Creek had four survey control marks set. The advantage of this smaller area was that I could dive into the FEMA map (left) and show more detail, the image on the right is a zoomed image of the ROS 22056 map from above showing the Alpine Creek marks.

...And the actual survey markers from Alpine

Drive-By Recoveries

It's difficult for me to pass up a recovery 🤷🏻‍♂️, even though I was really focused on finding the 23 marks identified in ROS 22056, I wasn't about to pass up a handful of Drive-By Recoveries that were indicated by the BM symbol (or Corner Symbol) on my USGS Topo Map. There were several that I couldn't find, but I did end up with a total of nine Drive-By Recoveries during this project, including a bonus "C" Stone near the G 737 RESET and one Section Corner mark that was right by the road!


So what started out as an unexpected Drive-By Recovery on my way back to the office from lunch one day, turned into a 3-week project of locating and documenting almost all of the marks that were noted on the Record of Survey Map No. 22056. Technically, I recovered all the marks that were SET on that survey, since the RCE 12725 mark was an existing mark, but I won't quibble over that detail 😉.

As always, my survey mark recoveries are the launching pad for learning new stuff, this project's topic was Flood Plains. I spent a lot of time reading up on the in's and out's of Flood Plain Mapping on both the County and FEMA websites. I seriously could write a collection of articles on that topic alone, but I have a hard enough time keeping up with documenting my hikes and survey mark recoveries! 🤣😂

Happy Hunting!


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