• Dale Hill

Woodson Mountain 2021 v3.0

Updated: Apr 1

Date: March 30, 2021

Distance: 4.9 miles

Total Elapsed Time: 2h 54m

Total Moving Time: 2h 19m

Summit Elevation: 2,894 feet

Elevation Gain: 1,313 feet

Trailhead: SR 67 Trailhead

Previous Ascents:

  • January 28, 2021 (SR 67 Trailhead)

  • January 1, 2021 (Blue Sky Ecological Reserve TH)

  • January 5, 2020 (SR 67 Trailhead)

Last week I saw a post from a fellow challenger who completed the San Diego Six-Pack of Peaks Challenge with a summit of Woodson Mountain 👍🏻Yay! 👏🏻 As I browsed through her summit photos I noticed she had found a Survey Marker that I'd never seen before 🤔 This immediately caught my attention since I had made two trips to the summit in January to recover all the survey markers that were still around (or so I thought!)


The "new" Survey Marker was labeled WOODSON and dated 1964, the brass disc was a U.S. Army Corps of Engineers (USACE) Marker and it was stamped "GIMRADA" in the space for the issuing Agency.


USACE GIMRADA Survey Mark for Woodson Mountain

Geodesy, Intelligence, and Mapping Research and Development Agency (GIMRADA)



GIMRADA, an off-shoot of the Army Mapping Service, was created in 1960, redesignated as the Engineer Topographic Laboratories (ETL) in 1967, and then became the Topographic Engineering Center (TEC) in 1991.


TEC did research in such fields as terrain analysis and geospatial data generation; developed imagery exploitation, rapid prototyping, and other systems; and conducted operations in areas such as geospatial information, crisis support, urban studies, and historical photo environmental analysis. Reflecting TEC's growing responsibilities in more diverse and technologically sophisticated areas, its name was changed to the Army Geospatial Center in 2009. It continues to support both military and civil works activities.

For military history buffs or those interested in the USACE, I also came across a comprehensive (378-page) PDF document entitled the History of the U.S. Army Engineer Topographic Laboratories (1920 to 1970) that is packed with information.

The Hunt is On



Random Rodentia 🤣

Unlike many other survey marks that's I've recovered, I could not find any location information for this one before heading out to look for it. For a mark set in 1964, I was really surprised that I only found 2 references to it online, two different Geocacher's had located it while searching for the primary Woodson station (DX5028). It's not uncommon for Geocachers to list the coordinates for their recoveries, often with a picture of their GPS device with the find, but neither of these listed the coordinates. The social media post where I first saw the disc simply had a "top-down" view of the marker with no mention of its location, other photos in the post were unrelated to the marker. I'm not saying that this is a "secret" marker or that no one else has found it, there is a trail that leads to the rock where it's mounted, so I'm sure plenty of people have seen it, it just doesn't have a presence online that I could find.


The EASIEST way to find it would have simply been to ask the person who posted the picture where it was, but that removes the element of the "hunt". True enough, a lot of the marks I have recovered are super easy to find because they are either registered in the National Geodetic Survey (NGS) data base, their approximate location is marked by an icon on a topo map, or they are clearly at a high point on a peak. Locating and researching old formal Surveys also provides detailed information that can save a lot of time in locating a particular mark, but you have to locate the survey...that's part of the hunt too.


After exploring what seems like every boulder at the summit that didn't require crazy-mad climbing skills, I finally found this one. I was seriously close to calling it quits but decided to check out one last area before heading down the hill. I was standing atop a large boulder looking around when I spied the mark on a nearby boulder. BAM - Success!

In the interest of preserving the "thrill of the hunt" for others, I've opted to only provide the close-up shot of this one, sometimes it's good to have a challenge and test your skills.

So if you're up for seeking this one out, happy hunting. I will add that given all the areas that I searched first, its location surprised me (and no, it's not on the high point), but I'll leave it at that 😉


Unexpected Recoveries Along the Way


I had two unexpected recoveries along the way, the first appears to be a Control Point (CP) used in a Traverse Network, the second is a chiseled "+" in the face of a boulder.


I was able to locate the CP on a San Diego County Topographic Survey (Photogrammetric) of Township 013S 001W, Sec 27, based on a photo taken June 22, 1999. This CP was labeled on the survey map as a Horizontal Control Monument (second-order or better) and a Vertical Control Monument (third-order). Without getting into all the advanced math, the lower the order number, the more accurate the mark is. Again, breaking it down to the basics, Horizontal controls deal with Latitude/Longitude while Vertical Controls deal with Elevations.


Topographic Survey Photo of Woodson Mountain Summit

Horizontal Control Monuments


I get a lot of questions about survey marks, "Why are there multiple ones on a summit?", "What does the triangle mean?", "What are the arrows for?", "Who put them there?", etc. When I got back into hiking last year, I knew nothing about these marks, they were just cool discs I occasionally found on peaks. The more I found, the more my interest grew and I began researching the history behind these marks, which ultimately evolved into a new hobby.


"The purpose of horizontal control marks are to accurately and permanently mark and reference point of precisely known latitude and longitude. The identification mark or names that are stamped in each disc must follow set rules to allow for properly identifying these stations at a later date.
At each horizontal control station a group or set of marks are established. These marks include the station mark for which the precise geographic position is known, reference marks for recovering or relocating the station, and an azimuth mark for use by local surveyors in obtaining a starting azimuth."

Source: Specifications for Horizontal Control Marks, Coast and Geodetic Survey Technical Memorandum USC&GSTM-4, April 1968, reprinted September 1976, page iii.


Vertical Control Monuments


Many people generally refer to ALL of the standard 3" Brass disc markers as Benchmarks, but a Benchmark (or Bench Mark) describes a specific type of Survey Mark (also called a "Control") that precisely measures orthometric height. The elevation is usually measured as height above sea level. Depending on its purpose and location, a mark may serve as both a vertical and horizontal control mark.


A vertical datum is a surface of zero elevation to which heights of various points are referenced. Traditionally, vertical datums have used classical survey methods to measure height differences (i.e. geodetic leveling) to best fit the surface of the earth.
North American Vertical Datum of 1988 (NAVD 88) consists of a leveling network on the North American Continent, ranging from Alaska, through Canada, across the United States, affixed to a single origin point on the continent.


Source: National Geodetic Survey website, Vertical Datums


Survey Point XP3


This tag is one inch in diameter and I almost missed it when I was checking out the boulder in search of the GIMRADA disc. This particular boulder was pretty big and if weren't for the excess epoxy around the mark, I probably would have overlooked it. I'd already been looking around on the summit for a half-hour and this was my first find of the afternoon. While it wasn't my primary objective, I was pretty happy to finally find something new.

Chisled "+" - Unknown Origin


This was the second mark I came across, it's on a boulder behind one of the towers, this was a very common way to mark survey points but it's the first one I've seen. I didn't remember reading of any chiseled marks on Woodson Mountain, but it met some basic criteria for an official mark so I took my pictures and figured I'd research it when I got home. Unfortunately, I couldn't find a reference to any chiseled marks on Woodson. 🤷🏻‍♂️ Still, I'll include it on my 'found' list. It's about 3.5 inches across and is oriented to the cardinal points N, E, S, and W. The mark is located on the face of the boulder (as opposed to the top) to minimize damage by the elements. There are no other extraneous markings around it, reinforcing my belief that it is a mark and not just some random vandalism. (I've seen examples of stone markings very similar to when people carve their initials in trees 😡)

Mission Accomplished!


My plan today was based on perseverance, I would explore as many boulders as I could between Potato Chip Rock and the primary summit boulder (where the WOODSON station disc and reference marks are located) that I considered likely mounting locations. Based on the timing of my ascent and other things I still needed to do today, I allowed myself an hour at the summit for pure searching time.


I was just about ready to call it a day when I spotted a disc on the boulder nearby the one I happened to be standing on, I'd found the USACE GIMRADA disc! I ended up spending close to an hour and logged an extra mile wandering around the top of Woodson Mountain just looking for this mark, but it was worth it.


Now I feel pretty confident that I've finally located all the survey marks on Woodson Mountain that are there to be found. 😉

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