• Dale Hill

Buried Treasure and More!

Updated: Feb 4

Today was a day dedicated to hunting for survey marks, often referred to as 'benchmarks' or 'controls'. The monuments that formalize survey points can come in all shapes and sizes but the 3" engraved and stamped brass discs are what most people think of first. I recovered (found and photographed) 14 marks and all were brass discs. I also found evidence of four marks, likely brass disks as well, that are considered lost. There's a distinction between not being able to find a mark in its supposed location and a mark actually being lost or destroyed, you'll see from the pictures below, there was good evidence that a mark existed at some time, but it's certainly gone now.

I had several "Firsts" with today's recoveries

  • Three new agencies that I had not previously recovered a mark from

  • A new category that I had not previously recovered (Tidal Benchmarks)

  • My first underground mark

Tidal Benchmarks

Quik-Recap: 5 discs recovered, 2 confirmed lost, 1 new agency: National Ocean Survey

My first objective for the day was to locate a Tidal Benchmark, this was a special category of marker that up to this point, I hadn't located yet. I had previously tried finding one of these in downtown San Diego, but it seemed the ones I chose to look for had likely been lost or destroyed in various construction projects. I hit the jackpot today, I found five!

Using the National Geodetic Survey (NGS) Explorer to give me a starting point, I decided to head to La Jolla, the Ellen Browning Scripps Memorial Pier and the surrounding area appeared to have several potential marks to find. The first two images below are screenshots from the NGS Explorer of the same area, both the map and the satellite view. Initially, the marks (or controls), are easier to identify on the map because the symbols stand out better in contrast to the relatively plain background. The control Types can be determined using the NGS Explore key. Clicking on one of the controls when you're in the Explorer calls up a pop-up with basic info about the mark and a link to its datasheet in the NGS database

Of course, not ALL survey marks are in the NGS database, and not all marks IN THE DATABASE still exist in reality, however, this is a good starting point. Taking time to read the datasheets will help determine which marks no longer exist, or at the very least, you can see the history of recoveries that have been reported to the NGS.

The National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) is responsible for the management of a national water level measurement program using a network of more than 200 continuously operating collection stations. According to the NOAA's User’s Guide to Vertical Control and Geodetic Leveling for CO-OPS Observing Systems, benchmarks are a vital component of the monitoring system.

All water level stations require a network of benchmarks. The number of benchmarks per network depends on the purpose of the stations. Currently all CO-OPS long-term stations to include NWLON (National Water Level Observation Network) stations require a network of ten bench marks with at least three of the marks having stability class B or higher.

This data is used for a variety of purposes to include mapping, dredging, tide predictions, long-term water level changes, and much more. The information also supports important U.S. Government programs such as the NWS Tsunami Warning System and the NOAA Climate and Global Change Program.

Benchmark Stability

A benchmark's stability class is determined by how it is mounted and its anticipated stability, examples of each class are:

  • Class A: Most reliable, expected to hold elevation well (mounted in bedrock [not boulders], or in a structure with a bedrock foundation)

  • Class B: Will probably hold elevations well (mounted using stainless steel rods that are driven to refusal, large man-made structures)

  • Class C: May hold elevation well but subject to surface ground movements (mounted in concrete monuments)

  • Class D: Unknown or questionable stability. (mounted into sidewalks, pavements, light structures, clay tile pipes, etc.)

NOAA Tidal Stations

Stations are organized into the states or regions in which the station is located. Within each state, the stations are listed in geographical order, following the contours of the coastline, allowing stations physically near each other to be listed together.

All of the marks Tidal Benchmarks I found today were at the La Jolla Station, tidal stations along the California coastline share the same '941' prefix, the last four digits identify the unique station. Because space is limited on the survey discs, sometimes the stamped identifying information is abbreviated. In the images below I have tagged each benchmark with its official designation and Permanent ID (if one has been assigned), you will see that the actual stamping on the disc may be some variation of the full descriptor.

As I mentioned above, these are the first Tidal Benchmarks I have found, three of the five are the first ones I have found that were issued by the National Ocean Survey (NOS), and DC1313 was the first one that I have found mounted with the aluminum logo cap covering a PVC pipe (the disc mounted a few inches below ground in the pipe)

Tidal Basic 1929

  • DC1308 (1964 Reset) was clearly lost/destroyed, I matched the Lat/Lon of the remaining stems (images above) to the coordinates in the datasheet and there's no doubt this is where DC1308 was located. There's no explanation why there are two cut stems less than a foot apart.

  • DC0987 (1949 Reset) was reported as not found during a 1967 recovery attempt.

  • DC1309 (1963 Reset) was reported as intact in 2008 and is located inside the entryway to an existing building, however, I was not able to verify this as the buildings were not open.

Today's Mystery Mark (Another New Agency!)

BOCK Reference Mark 1

While scouting around Scripps Institution of Oceanography looking for tidal benchmarks, I caught this disc out of the corner of my eye.

Mounted on the top of a short retaining wall next to the sidewalk on the north side of Discovery Way, it didn't point anywhere. Usually, reference marks are located within 20 feet of the station disk they refer to. Too, they usually have a directional arrow pointing towards the station. I looked around the general area for the station or another reference mark but came up empty. I thought this was pretty cool that it was a Scripps Institution of Oceanography disc, but I've been unable to find any solid information on it. The closest that I've been able to come is that it may somehow be related to Dr. Yuheda Bock Ph.D., Researcher at the Institute of Geophysics and Planetary Physics / Senior Lecturer, and Director, Scripps Orbit and Permanent Array Center.

Buried Treasure (2 Recovered and 1 Lost)

RM 2 was the 'easy' find

The Triangulation Station BALL and its Reference Marks seemed like an easy recovery, it was on a small knoll along the La Jolla Trail, not too far from the Gliderport and just east of the trail down to Black's Beach. Since I was driving right past it on my way to Torrey Pines State Nature Reserve, I opted to stop for a quick recovery. I was able to find parking in the Gliderport lot and it was a short walk over to the station location.

From the datasheets, I expected that Reference Mark 1 was gone and Reference Mark 2 was significantly mutilated.

As expected I found Reference Mark 2 quickly, it's about 2" above the ground, mounted in concrete. All the reports of it being mutilated were spot on! I could barely make out enough to determine the 1887 date, the name BALL, and the ends of the arrow. I located the concrete-filled iron pipe that held the latest version of Reference Mark 1, the pipe was laying on a side-hill at almost the precise coordinates given for the mark, the disc had been cut off.

The information about the station disk was a bit confusing, early (1887) reports talked about the mark being a bottle buried 20" deep with its neck pointing up, and some stakes and cinders marking the spot on the surface.

In 1914, a standard bronze triangulation station disc was set in concrete on the surface (leaving the original sub-surface station mark, the buried bottle, undisturbed)

The BALL Station Disc 1949 Reset

A recovery description in 1959 noted that there had been a Reset of the station disc in 1949, but there were no notes describing the event. The only way they knew was that they found the station disc stamped "Reset 1949". It's unclear what became of the first station disc set in 1914.

Finding this station disc took some work. It clearly wasn't visible just walking around, even using the bearings from the reference marks. It was further complicated as one of the descriptions said the station was located 'just left' of the line indicated by RM 2. (perhaps because when the disks were originally mounted, they didn't want to damage or disturb the sub-surface mark?) Keep in mind, the 1949 Reset disc was the third documented station marker set for this site. The first two being the original sub-surface bottle (supposedly still 20" underground), and the first triangulation disc in 1914. There really was no way to know how accurate the bearings from RM 2 still were. I made a trip back to my truck to get a tool to probe and dig with as well as a pair of gloves. I poked around in the dirt, dug starter holes when I felt some resistance, and came up with a lot of rocks. Based on the most current recovery descriptions I was anticipating the station disc to be anywhere from ½-inch to 6-inches below grade. After spending almost an hour measuring, re-reading descriptions, probing, I finally located it a couple of inches down, under some chaparral. My buried treasure!

Two Drive-By Recoveries

Never one to pass up a Drive-by recovery when it was safe to pull over and snap a few pictures, I had two of these today, one along Wildcat Canyon Road as I was headed to Scripps and the second on La Jolla Shores Drive on my way to search for the Ball station. These are just more of the typical 'found along the road' marks, but I still like to add them to my collection.

Torrey Benchmark, Elev. 367 ft. (TPSNR)

I spent the better part of the afternoon hiking the network of trails in the Torrey Pines State Natural Reserve, one of my early stops was at the High Point Overlook to recover the Torrey Triangulation Station Disc and the two Reference Marks (labeled Torrey Pines). All three of these marks were in exceptional condition, especially given their location in a highly visited location. I'll have more about the hike itself in my trip report, but here are the three marks I found.

Another New Property Corner (3rd New Agency!)

I have found quite a variety of corner markers so far, and it's not uncommon that they are set by licensed Land Surveyors, however, this was the first survey mark that I have found issued by the California Division of Beaches and Parks, a predecessor agency of the current California Department of Parks and Recreation. I haven't looked up the actual survey that resulted in this monument, but it's likely to have occurred in the late '50s or early '60s. What I find interesting, is that doesn't align with a typical section boundary so it may have marked a corner for the State's property at that time. This marker is located 50 or so feet down an unnamed use trail that appears to cross over from the Red Ridge Loop Trail to the Margaret Fleming Nature Trail in the Torrey Pines State Nature Reserve Extension. You can see from the map screenshot, it is in the opposite direction of an expected corner location, I did initially check that out, but I came to a sheer cliff before reaching the intersection marked with the "24" on the map, it was purely on a whim that I ventured down the use trail where I ultimately located it!

Torrey Pines State Reserve High Point, Elev. 407 feet (1 Destroyed)

I was surprised to learn that the High Point in the Torrey Pines State Reserve was NOT located in the principal part of the reserve where the Torrey Benchmark was. The Red Ridge Loop Trail in the TPSNR Extension leads to the designated High Point. As I approached the high point I came upon the final Survey Marker that was Lost or Destroyed. This one didn't have a registered survey mark, but you can clearly tell there HAD been one there.

Phew! There you have it! One day, 14 marks, 4 lost/destroyed marks, my first Tidal Benchmarks, 3 new agencies identified, and a mark that I had to dig for! My best Scavenger Hunt day to date!

Disclaimer: Survey markers may be located on private property, please respect the landowner’s privacy and property rights while searching for markers. Additionally, 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!


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