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  • Writer's pictureDale Hill

Yosemite SMASH

On July 21st, I checked off a big item on my bucket list; ascending Half Dome by the cable route. It was an epic day, to say the least, over 16 hours and 16.68 miles of hiking through Yosemite National Park, 5,020 feet of vertical gain, and the challenge of going up and down the smooth East face of Half Dome. The trip report, Half Dome via The Cables, has been the most viewed article on my site; if you haven't checked it out, it's a great read, and I was humbled by the vast number of positive reviews, DMs, and kind words such as these:

"GREAT was as if you were standing right next to me, telling me about your are a good writer...after many experiences in Yosemite, this was especially nice reminder of her the video at the summit...Happy Trails, Friend." ~ Mona
"Wonderful account of your hike and gorgeous photos. I read every bit." ~ Megan
"The best pictures and story yet, thank you from an old man that can’t make the trip anymore." ~ Randy

My Half Dome hike was amazing; however, it was just one day of a five-day adventure to Yosemite. When I wasn't driving, I was either exploring the Park, doing smaller hikes, or looking for survey markers. This article is dedicated to the Survey MArk Scavenger Hunt (SMASH) that spanned my five-day vacation.

If you've been following me for any time, you know that over the last couple of years, I have made a hobby of locating and documenting geodetic survey marks. This process is called "recovering" a survey mark and consists of finding its location, verifying the condition of the marker, documenting the recovery with photographs, and (in the case of some survey marks) submitting the findings to the National Geodetic Survey (NGS) to update the national database of registered survey marks.

I maintain a database of all the survey marks I have recovered; what draws me as much as discovering these marks is learning the marks' history, science, and back story. I have learned much about the regions, cultures, and people surrounding the marks through my recoveries.

With the wide variety of survey marks I recovered throughout the week, the most logical presentation is to take them day-by-day (mostly) in the sequence I found them.

Tuesday, July 19

Tuesday was my travel day; depending on traffic, I expected between seven and eight hours on the road. Stopping to search for survey marks adds a lot of time, so I wanted to find potential recoveries close to the roadside and consolidated in one general area. When traveling, the first level of reconnaissance I perform is looking for REI stores; most REIs have a custom survey marker on the sidewalk at the main entrance to the store. I Googled REI Stores in Southern California and looked to see if there were any close to my route to Midpines; BINGO! The Fresno store was on my way!

Using the NGS Data Explorer tool, I centered my survey mark search on the REI store location, focusing on marks close to the route I would be driving to reach REI (SR 99 to SR 41). There were 150 listed survey marks within a 10-mile radius of the store, too many for the limited time I had, but I picked a handful at random and created waypoints for them in my GAIA GPS app.

150 listed survey marks within a 10-mile radius of REI in Fresno! Too many to choose from 🤣

The most recognizable type of survey marker is a brass disc stamped with information identifying the mark. Finding survey marker discs in a major urban setting can be challenging, as many are destroyed or covered up during development. The NGS uses 11 broad categories to identify survey marks; the 3-4" brass discs are but one. Within those 11 categories are more than 130 different types; the first two marks I selected randomly on my map were elevated tanks in the category "Tanks and Towers."

Survey Marker Type 53: Elevated Tank

The great thing about tanks and towers is that they are easy to verify using the satellite view on the Data Explore map. The satellite view uses Google Earth images, and you can drop down to street view to "look around" for your mark. It was easy to verify that both of these water tanks were intact from the comfort of my home office as I prepared my list of survey marks to recover.

You may wonder how a water tank can be considered a survey mark. Survey marks are also referred to as stations. In basic terms, a station is a definite point on the Earth whose location has been determined by surveying methods. This type of station is called an intersection station; Intersection stations are objects that would be difficult to occupy with surveying equipment or whose positions can be determined with sufficient accuracy without being occupied. In this case, the apex, or top of the tank, is the point of intersection on each of these tanks. A surveyor would not need to physically set up their equipment on top of the tank in order to use it as a survey point. For me, these are both cool AND easy peasy recoveries!

HPGN CA 06 06 ~ PID: GT2133

Almost across the street from where I stopped to photograph the CALWA United Grocers Ltd. Tank was a standard California Department of Transportation High Precision Geodetic Network (HPGN) Station 06-06, clearly marked with two witness stakes, so another easy recovery.

Heading North on SR 41 following the directions to REI, I had picked two stations on the way that were set on the sidewalk; both were on bridges that spanned the 41 and were easy to verify using Google Earth street view.


With almost 1,200 survey marks in my database, I am still amazed when I make new recoveries; these two discs were the first two that I've recovered that were stamped "CA Spatial Reference Center." According to its website, The California Spatial Reference Center (CSRC) is responsible for “Establishing and maintaining an accurate state-of-the-art network of GPS control stations for a reliable spatial reference system in California.” Well, THAT'S a mouthful 😂

For the scientifically inclined or the naturally curious, the website provides a lot of detailed information that is well beyond the scope of this article. Still, I found a reference to uses of real-time geodetic information that I hadn't considered before: intelligent vehicles, precision navigation, and emergency early warning systems. These discs are passive reference points in the overall system and are just as important as the active stations that continually transmit positional data. I feel another excursion down an internet rabbit hole coming on! 🤔

REI, 7786 N Blackstone Ave, Fresno, CA 93720

As expected, I recovered the survey mark at the entrance; REI has a custom survey marker cast with the Co-Op logo and the traditional triangle in the center of the disc, similar to a triangulation station marker. Each disc is stamped with the store's location, elevation above sea level, and the date the store opened. Not all stores have the markers; for example, when I spoke with the manager at the Northridge, California store, he said they opened in 1991 before the Co-op began using the custom survey markers.

Of course, I can never pass up picking up a few essentials at REI, and today was no different. I loaded up on various snacks to take on my Half Dome hike. I was also looking for a specific safety lanyard to use with my climbing harness when I ascended the cables at Half Dome, a PETZL Scorpio Vertigo Via Ferrata shock absorbing lanyard. Unfortunately, this item is generally only available online; while it may be shipped to your local store, I needed it immediately. Ah, the pain of poor planning 🙄. (Note: I ended up ordering one on Amazon, but it wouldn't arrive until after I returned from my trip.)

While back in the climbing department, I noticed a survey marker in the middle of the aisle! This is the first marker I have found INSIDE an REI! 👏🏻😊 I had heard rumors that some stores had them inside, but I'd yet to find one. Of course, it bears the same markings as the one outside, but it was still very cool to find this one.

After a lunch of Singapore Street Noodles at the nearby P.F. Changs restaurant, I was back on the road headed for Midpines via SR 41, SR 49, and SR 140. While planning my trip, I had set waypoints for several HPGN stations along my planned route between Fresno and Midpines and stopped to recover CA HPGN D 06 SG ~ PID: AC6106 on the way.

There were a string of traditional Benchmark discs in the 288 and 683 numbered series; however, I didn't create waypoints for those as they required frequent stops, and I didn't have the time to look for all of them. As it turned out, I happened to easily spot a mark (W 683 ~ PID: HR0455) on a culvert headwall in a spot where it was easy to pull off the road to make the recovery.

Mindful of the time, I called it quits for the day with nine recoveries and headed to the Yosemite Bug Rustic Mountain Resort (that I affectionately referred to as the "Bug"), where I'd be staying for the rest of the week and meet up with my friends for dinner.

Wednesday, July 20

My original plan for today was to spend the day in Yosemite National Park, looking for a series of survey marks I had identified during my initial planning for the trip. Plans are made to be changed! I realized too late that I would need a safety lanyard for my climbing harness on tomorrow's hike to Half Dome. I looked for a lanyard at REI yesterday, but they didn't have them in stock and wouldn't be able to have one in the store in time for my hike. I planned to check local gear shops and sporting goods stores today to find what I needed.

Long story short, I ended up back in Fresno to purchase a lanyard at Home Depot. While not as lightweight as a hiking-specific lanyard, I found one that would work. The downside was that I spent all morning driving and going store to store. After grabbing lunch, I headed back to Yosemite with the idea of spending the afternoon looking for marks inside the Park.

Since I was retracing yesterday's route, I decided to stop and look for the remaining High Precision Geodetic Network (HPGN) discs that I marked on my map; finding all three.

All three of these stations are HPGN Densification stations. According to the NGS, an HPGN is a designation used for a statewide geodetic network upgrade. The generic acronym HARN (High Accuracy Reference Network) is now used for both HARN and HPGN and was adopted to remove the confusion arising from the two acronyms. A HARN is a statewide or regional upgrade to the accuracy of NAD 83 coordinates using Global Positioning System (GPS) observations. Many of the survey marks used in this network are named HPGN stations.

The original spacing for the HPGN was 40 miles (64 km). To improve access to the HPGN, densification monuments were set at 10-15 mile (16-24 km.) spacing, providing more control points and increasing network accuracy.

The final two finds for today were pure Drive-By Recoveries. I thought it would have been a cinch to locate the station disc for FOUR CORNERS since I easily spotted FOUR CORNERS RM 2 ~ PID: DA9941, which pointed directly across the road to where it should have been. However, the road was being widened, and there was considerable new landscaping; I imagine the station disc and reference mark one had been lost or buried. I spotted the other unnumbered Benchmark disc on a culvert headwall just outside of Mariposa; for lack of any uniquely identifying information, I have identified it by its postmile location on SR 140.

I reached the El Portal entrance to the Park late in the afternoon; after sitting in the traffic queue for an hour and a half, I reached the sign that said "60-minute wait from here." Realizing I wouldn't have enough time to search for survey marks in the Park AND get back to the hostel at a reasonable time, I got out of line, turned around, and headed back to the "Bug."

Thursday, July 21

Today was a full day dedicated to hiking Half Dome; I left the Bug a little after 4:00 a.m. and didn't return until just after midnight. You can follow the link provided at the beginning of this article to read my full trip report for that adventure. 😊

Friday, July 22

As I noted above, plans change. My original plan for today was to hike to Clouds Rest and recover the survey mark at the summit. After yesterday's hike, doing another 13 miles with more than 3,000 feet of vertical gain didn't sound as appealing as it did in pre-planning. I opted to make Friday my "Park" day.

On my way to breakfast, I spotted two more Drive-By Recoveries, another unnumbered Benchmark on a culvert headwall, and a postmile marker that had two witness stakes and a witness sign nearby.

After breakfast, I drove to the park and began looking for the survey marks I had created waypoints for on my map. Due to the one-way roads entering and leaving Yosemite Valley, I made several loops around, stopping to take pictures of the scenery as well as looking for survey marks.

Finding parking near a particular recovery could be challenging and often required a few passes before I could find a spot. Still, I wasn't in a particular hurry, so I enjoyed the beautiful day and checked off the marks as I found them.

U.S. Department of Agriculture Bureau of Public Roads

Today, two of my favorite recoveries were Bureau of Public Roads pipe cap markers. I found it cool that these were painted gold and still in amazing condition, one from 1926 and the other from 1927. I use chalk to call out the engraving on survey markers to make them more readable. However, the first disc was legible without the chalk!

27 S = 3964 ~ PID: HR0710

The oldest mark I found today (and on the trip) was a U.S. Geological Survey Benchmark dated 1905. This was located on a boulder near the old church on Southside Drive. It was difficult to read the stamped elevation, even with the chalk to highlight the information. However, the "27", "S," and the date are visible around the initials B.M.

Department of Interior National Park Service

Two of my "Surprise Proximity Recoveries" were unnumbered National Park Service Discs; each was located near a manhole cover, close to where I was looking for other marks. The first was noted in the datasheet as due west of S 20 ~ PID: HR0713. S 20 appears to have been destroyed in a fire (it may have been dug up or buried). It was referenced as being in a copse of pine trees, all burned down, and the ground turned over, probably during efforts to put out the fire. The second was on the Pohono bridge, opposite a Gaging Station disc I recovered.

Gaging Station, Site ID: 11266500 Merced R A Pohono Bridge NR Yosemite CA

Yosemite National Park (YNP) contains 21 meteorological stations, 18 automated "real-time" stations, and three manually operated. The gaging station on the Merced River near the Pohono Bridge is one of five river gage locations operated by the U.S. Geological Survey in the Park and is also one of the oldest stations providing valuable data. According to the Park's website, this information was originally collected to answer water supply, flood, and weather forecasting needs. Over time, data expanded to include fire management and climate change impacts.

To view real-time water and historical data back to 1916 for this station, you can visit the USGS Water Data page for Site ID: 11266500. The Department of the Interior U.S. Geological Survey Gaging Station and Reference Mark discs are standard and don't identify the specific station name or ID on the disc. Now that I know several more gaging stations in the Park, I'll have to add them to my list to look for the next time I visit.

Odds and Ends

The next two survey marks I found today were a little different. The first is an unnamed reference mark stamped with an arrow pointing toward the station it references and the distance to said station. I was expecting to find mark S 26 ~ PID: HR0704 located just off the back patio of the Ahwahnee Hotel. During my research of the mark, I viewed pictures of the mark and its location near a large pine tree on the patio. The tree had long been cut down, and there was no evidence of the concrete monument or the S 26 disc. The datasheet did not mention a reference mark, and there is no other identifying information stamped on the disc, so it's hard to determine if this was related to S 26.

The second find was a concrete witness post for S 19 ~ PID: HR0698. Normally I wouldn't document a witness post by itself; however, this particular concrete post was called out in the datasheet with the notation that the adjacent pine tree had encroached over the monument and marker. I poked around at the base of the tree and cleared leaves and sticks away in hopes of seeing at least part of the concrete monument holding the survey mark but didn't find anything. Unfortunately, I didn't have anything to probe into the ground with. Perhaps next time, I'll come equipped with the right tools to make a more thorough search.

The Wawona Tunnel

According to Wikipedia, At 4,233 feet (1,290 m) long, The Wawona Tunnel is the longest highway tunnel in California and is bored directly through the granite bedrock of the mountain. As it exits the Park, Wawona Road turns into SR 41, one of the three main entrances to Yosemite Valley. In 1934, the year following the completion of the tunnel, a USGS Benchmark disc stamped with the elevation was placed at each entrance to the tunnel.

Driving further on Wawona Road, I noticed a huge smoke plume from the fire and stopped to take pictures of it. At the time, I thought it was the Washburn Fire flaring up again, but I would learn on my way back to the hostel that it was a new fire, the Oak Fire, that started about 4.5 miles from the resort where I was staying!

As I was leaving the Park, I paused to get a photo near the entrance sign at El Portal; notice the difference in hue caused by the smoke in the air combined with the afternoon sun!

There were large electric signs outside the Park indicating that Highway 140 was closed; I was unaware of what was going on, so I stopped at a gas station near El Portal and learned of the fire in Midpines. Concerned if I could get to the hostel, multiple people assured me the fire was closer to Mariposa and that I would be able to get to the Yosemite Bug. The first image was my view as I turned into the entrance road of the resort. The remaining photos were taken from the Ridgetop parking area above our dorm unit.

Water and power at the Resort had been out since sometime on Thursday (before the fire) and were still out, so I decided to leave Friday night, driving to Fresno, where I got a hotel room for the night.

Saturday, July 23

Today was "the drive home." I left Fresno late morning and planned to stop in Frazier Park to complete one of the hikes on the 2022 SoCal Six-Pack of Peaks Challenge: Sawmill Mountain. This hike went over Mount Pinos on the way to the Sawmill summit, and I still had one survey marker to find on Mount Pinos. However, that hike, and the ten survey marks I recovered on my way there, will be covered in a separate trip report for Mount Pinos and Sawmill Mountain. 😉

I did have a single recovery on the drive after leaving Fresno; I had stopped to get fuel and some snacks when I noticed a survey mark not too far from the freeway on-ramp. I made a quick stop and recovered HPGN D CA 06 NJ ~ PID: AC6111, another densification station. This was just a little obvious, as it had about six different witness posts or flags marking it! 🤣


Overall, this had been an amazing and eventful week; I had completed a bucket list hike by climbing Half Dome via the Cables, did a lot of sightseeing in Yosemite National Park, avoided a major California wildfire, and recovered a total of 38 survey markers, 28 listed in this report, and 10 to be covered in my Mount Pinos and Sawmill Mountain trip report. One thing is for sure; I'll be returning to YNP to do a lot more hiking and look for more survey marks! 😊

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