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  • Writer's pictureDale Hill

Joshua Tree SMASH

Total Marks Recovered: 32

Confirmed Lost/Destroyed: 2

Not Found: 1 (witness post present)

Discs Recovered: 26

Non-Disc Type Recovered: 3 (1 pipe cap, 2 Hexagonal marks)

New Agencies: 4

Notes: New Agencies

  • U.S. Department of Interior, National Park Service

  • Bureau of Water Works and Supply, DWP, City of Los Angeles

  • Riverside County

  • Bureau of Reclamation

On a whim, I decided to do a Survey MArk Scavenger Hunt in Joshua Tree today. Several months ago I had come across a blog post that contained a photo of a very cool Gravity Station that was located within the Park. Of course, I wanted to make that recovery so I plotted it out, entered it into my GAIA GPS as a waypoint, then searched the nearby area for other potential recoveries. Still being somewhat limited in the hiking department, a Road Trip to JTNP to look for survey marks sounded like a great way to spend the day.

One thing about most of my SMASH outings, I spend more time in the truck driving from point to point because the distance and routes between marks usually make hiking impractical. Today, there was the added factor of end of August temperatures. Starting out, I was recording temps just under 100º but by midday, it was getting pretty toasty, capping out at 119º 🥵.

Still, the day was a huge success, I recovered 32 survey marks and made lots of "new" recoveries. For the purpose of this article, I've grouped my recoveries together based on the type of mark rather than presenting them in the order that I found them. If you have an interest in a particular type of mark, I've provided the following internal hyperlinks that will jump down to a specific section.

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National Park Service Marks

This collection of Department of the Interior (USDI), National Park Service (NPS) numbered survey marks stamped "JT" was an unexpected find. I had stopped near a service road to look for a benchmark identified on my topo map as E 1254, elevation 2,826.5 feet, according to the NGS Data Explorer it was listed as PID: DW0381, there was also mark E 727 (PID: DW0380) nearby. I didn't find either of the "E" marks, but I came across this 1 ½ inch disc stamped USDI NPS and numbered JT-53.

Once I was paying attention to lone metal fence stakes, these became pretty easy to find and I located two more of this style disc later in the day, JT-56 and JT-60.

Not only were the USDI NPS marks another "first" for me, but I also found that they used two different styles of marks. The first ones were the smaller, smooth discs with the information stamped into the surface. The second type was a 2-inch cast disc so all the standard information was raised lettering, the mark's unique identifying information was stamped in the center of the disc.

JT-41 was located very close to Benchmark C 727 (PID: DW0491), at first, I thought it was another mark related to C 727 based on the legend on the topo map, but these NPS survey marks are not identified on the topo, so it was likely just a coincidence.

As you can see in the close-up photo, the concrete monument this is mounted on has definitely seen better days. This also had four bolts evenly spaced around the mark that were sunk into the concrete, I'm not sure exactly what they're for, maybe some type of cover? The chalk doesn't work really well on the raised lettering, but it does clearly call out the center stamping, again, another unexplained element of JT-41 is the additional stamping of "123". I found JT-40 about 3/10ths of a mile (.5 km) NNE of JT-41, about the same distance from the centerline of the road and clearly marked with a witness stake. JT-40 was in much better condition and easier to read.

Lost/Destroyed Marks

My master plan for the day was to drive to Joshua Tree and head to the survey mark furthest away first, then slowly work my way back through the Park and look for the other ones on my list. I TRIED to minimize stopping for Drive-By Recoveries on my way out simply because I wanted to make sure I made it to a few particular survey marks. Having said that, some marks were just "low hanging fruit" and it didn't take much time to stop and make the recovery.

As I drove past this spot (also marked by a BM symbol on my Topo) I easily spotted the concrete monument in the rock so I pulled over to check it out. Unfortunately, as you can see from the images below, the survey mark that was here, is now lost. Based on the latitude and longitude of this monument, I was able to identify this as TBM 111 (PID: AM1803) in the NGS database.


I had identified several survey marks in the Coachella Valley, on the Torres Martinez Indian Reservation, including named stations set by the California Department of Transportation and others identified as GPS on Benchmarks Priorities. Many of the marks I was looking for were right along the roadside and should have been pretty easy recoveries.

One of the most common causes I see for lost or destroyed survey marks is new construction, whether it be the development of houses, commercial properties, or road improvements. Many of the marks I had on today's list fell victim to aggressive grading of the shoulder along the roadside. There was enough of the culvert wing wall remaining, and the obvious hole created by the removal of the concrete monument, to determine MIRANDA was lost. The hole in the ground matched up with the "to reach" directions in the datasheet that gave its location in relation to the culvert wing wall.

In many cases, the grading in this area was the width (or more) of a full lane of traffic on either side of the road, in other locations the spoils from the grading were piled alongside the graded area to form a berm 2 to 3 feet high, effectively burying any marker that may have been offset from the roadway. I was a little disappointed by this as I went from location to location, but what can you do right?

I called this one a "Quasi-Recovery" 🤷🏻‍♂️It was annotated on the map as a third-order (or better) Horizontal Control Mark and when I drove up to it I was excited to see the Caltrans witness paddle. This is the first witness paddle that I have found that had been labeled "Survey Mon" (faded, see the second image) and had the circle and square images on it. I looked all around the paddle for signs of the survey mark, but couldn't find anything. I didn't have a probe or a shovel with me to dig around, so the next time I'm out that way, I'll return prepared to do a more in-depth search.

I was intrigued by the markings on the paddle, up to this point I was used to seeing these used as mile markers along the road, but as I learned, they are used for a lot of other purposes. The Circle identifies this as a Right-of-Way mark (R/W or ROW depending on who is doing the shorthand) and the Square denotes a Monument. Additionally, if the paddle includes a Triangle, that means the nearby survey mark is also a Control Point.

A Mark I Just HAD to Recover!

As a Personal Trainer, I knew that I had to recover the Triangulation Station named: LAT, mainly because the disc is stamped TRI LAT 🤣 okay, so the pun may be lost on most people, but I found it funny 🤷🏻‍♂️ I was only able to locate the main station and Reference Mark 1. I couldn't find any signs of a second reference mark or a supposed Gravity Station that nearby.

GPS on Bench Marks

All of these recoveries could also qualify as Drive-By Recoveries as they were all marked on the topo map with benchmark symbols and were very easy to locate. They are all either traditional benchmarks or vertical control marks, I was excited to recover B 1255 as it was the first disc that I've found from the Bureau of Reclamation! It was also good to find a variety of GPSonBM priority levels.

It should be noted that IMP 2 RESET may not qualify as a GPSonBM recovery. Technically, this Reset disc is dated 1979, mounted in the bridge abutment, and is not cataloged by the NGS, the original IMP 2 was dated 1968, was supposedly mounted flush with the ground, and was identified with PID DX0525. I need to update my database and re-label this as PID: N/A then report DX0525 as "Not Found".

DX0525: IMP 2 (2 km, Priority B-2 Observation)

DX0604: B 1255 (10 km, Priority A-2 Observation)

DW0363: M 1254 (10 km, Priority A-2 Observation)

DW0376: H 727 (10 km, Priority A-1 Observation)

DW0489: A 727 (Secondary Mark)

Gravity Stations

YAY! 😊Honestly, I built this entire trip around recovering these two Gravity Station marks, It was SO COOL to finally find one of these funky Hexagon shaped survey marks. If you've been a faithful follower of my hiking/survey mark activities, you may recall that I found evidence of one of these Gravity Station marks on Mt. Pinos while hiking to Sawmill Mountain for the 2021 SoCal Six-Pack of Peaks Challenge. If for some reason you missed that trip report, I have a dedicated article about the survey marks I found on Mt. Pinos 👉🏻 (click here to view the article in a new window)

Soooo, What's a Gravity Station?

Consider this a launching pad for further research 😉 and welcome to my world of continuous learning spurred by the survey marks that I recover. here is a snippet from an article that was prepared in 2007 for the 200th Anniversary of the National Oceanic and Atmospheric Administration (NOAA). The article gives a nice synopsis of the evolution of the National Spatial Reference System (NSRS) beginning in 1807 with the Survey of the Coast, a predecessor organization of NOAA, which was formed and given the mandate to map the shoreline and coastal features of the new United States.

Gravity Observations Begin In 1872, the Survey began making gravity observations. Initially, the Survey developed its own gravity instruments but later purchased state-of-the-art instruments. Gravity measurements were made at selected locations all across the country. Some observations were made on existing benchmarks and some on special gravity survey disks and gravity reference mark disks. This extensive network of gravity observation stations is used in combination with other data to model the geoid (an equal gravity surface, approximating mean sea level) and geologic structures. Some of these gravity stations serve as reference stations for relative gravimeter surveys. Another subset contains the absolute gravimeter stations, where very precise and repeated measurements are made to determine geologic changes (e.g., elevation, water-table, magma movement).

The unique hexagonal markers were used between c.1936 and c.1972, newer Gravity Station markers were standard discs similar to other NGS markers. It's not really a surprise that this marker was stamped 1976, the surveyor who set it was likely using up the existing inventory they had on hand.

Station PBB 17 A +.101 was found nearby, the "+.101" denotes the distance (meters) it was from the primary station PBB 17.

This U.S. Department of the Interior Survey Mark was a bonus find on the same rock where the Gravity Station was!

More New Recoveries

This really was a day of new recoveries, these two marks were "firsts" in that they were issued by agencies that I have not previously recovered survey marks from. The City of Los Angeles disc was interesting, I expected the DWP designation but not the Bureau of Water Works and Supply, so that was cool. B.M. 603-9-68 was the first disc I've found issued by Riverside County, this one was mounted in a pretty serious concrete monument!

Section Corners

I never get tired of looking for section corners 😊 there have to millions of them across the country and if you have the patience to walk the grid, you will very likely be rewarded with some cool recoveries. I've made no bones about it, I really like the old U.S. General Land Office Survey pipe cap markers, maybe it's just that they all date back to the late 1800s and early 1900s.

Most places I go nowadays, I always have my PLSS grid overlay up on my GAIA GPS USGS Topo map, if there is a potential corner marker within a mile of the road and it's not on restricted or private property, I'm going to pull over and look for it! 🤣 Because I had so many other marks on my radar today, I only recovered one corner mark, but it was in excellent shape and exactly where it was supposed to be.

The Rest of the Drive-By Recoveries

There really isn't much of a story behind all the Drive-By Recoveries (DBR) I made today, except that next to section corners, these are potentially some of the easiest recoveries to make. The more remote (or protected) the location, i.e. on Parkland such as in Joshua Tree National Park or in the Anza-Borrego Desert State Park, the more likely it is that you'll find a good witness stake to mark where the monument is. DBRs are not necessarily a sure thing in urban areas or where there has been a lot of recent development. Today I separated my DBRs by the type of mark, this first batch was all Vertical Control Marks issued by the National Geodetic Survey, and with only one exception, were all set in 1974. The second type of mark is the true "benchmark" disc issued by the U.S. Coast & Geodetic Survey.

Vertical Control Marks

You can see from the images below, these are set in a variety of ways, some are below grade in a PVC sleeve, while others are mounted in bridge abutments, rock outcroppings, or concrete monuments.


Most benchmark discs of this nature are generally mounted in concrete monuments or in rock outcroppings with witness stakes or signs nearby.


What an amazing day! I spent so much time looking for survey marks, that I really didn't leave myself any time to explore the easily accessible trails around where I was in the Park. I will definitely go back and do some camping and hiking in the Park, this is just one of those amazing areas that I have yet to explore. (Adding to bucket list as we speak!)😉

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