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  • Writer's pictureDale Hill

Obsidian Butte SMASH

Updated: Dec 18, 2021

Recovery Date: December 11, 2021

Total Marks Recovered: 35

Discs Recovered: 32

Non-Disc Type Recovered: 2 (1-Washer, 1-Concrete Post)

Lost/Destroyed: 1 *

GPS on Bench Marks Priorities: 9

Note: Station mark OBSIDIAN was likely Lost/Destroyed, but there was no concrete evidence of its presence, so it would be considered not found but likely destroyed.

Today's Motivation: Obsidian Butte

While hiking through the Los Coyotes Indian Reservation and Anza-Borrego Desert State Park last month (read that trip report here 👉🏻 Cody Benchmark - Peak #94) with Gina, Maya, and Alberto, Gina was telling me about a trip she and Maya had made to Obsidian Butte and the Sonny Bono National Wildlife Refuge that sounded very cool. I made a mental note to check it out when I got home.

The butte is at the southeast side of the Salton Sea and was about a two-hour drive from home, but I noticed there were LOTS of survey marks along the route I would take to get there, so I planned the trip as a Survey MArk Scavenger Hunt (SMASH) for an upcoming weekend.

Life has a nasty habit of getting in the way, and it ended up being almost a month before I could actually head out there. This morning I left the house a little before daybreak and planned to take the 78 through Julian, down Banner Grade, through Ocotillo Wells toward the Salton Sea where it connects with the 86, then continue south to Westmoreland where I'd pick up surface streets the rest of the way. I'd scout out Obsidian Butte first, then focus on recovering survey marks on my drive back home.

That sounded like a good plan and had I left the house an hour earlier, I probably would have stuck to it. However, given my later start, I had good daylight when I rolled through Santa Ysabel and I was determined to locate a pesky mark that I'd failed to find on two prior occasions...the third time is the charm, right? 🤷🏻‍♂️

SY 97: DX0237 (GPSonBM, Secondary Mark)

This mark could easily be subtitled "the one that got away" 🤣 This particular mark is along SR 78 in Santa Ysabel (hence the "SY" numbering) and it ended up being closer to an old concrete road that paralleled the 78 at the north end of Quanai Canyon. For some reason today, this was a pretty easy recovery, the first two times I stopped to look for it, not so much.

I had previously dropped a waypoint in GAIA based on scaled coordinates (plotted from a map, not verified by GPS) and I thought that would get me close enough. I didn't have the printed datasheet with me, but I had made some notes about where it should be based on the "to reach" description from the datasheet. On both previous occasions, I was working within a reasonable radius of the scaled location, but I kept coming up empty-handed.

Today I parked in a different turnout and had to approach my waypoint from a different direction, on my to that point, I walked right past the witness stake! The spot I was working in before wasn't even close to this witness stake and from my previous location, the witness stake was obscured by heavy brush. Go figure. The monument was completely covered in leaves, dirt, and sticks, I had to knock a lot of the brush down and kick around in the leaves for a while to finally locate it, but at least I knew I was finally in the right spot! Sometimes you're good and sometimes you're just lucky.

Excited to have finally made this recovery, I was energized to start searching for more marks right away. Given all of my various trips out to the desert to look for marks though, I've pretty much recovered the "low-hanging fruit" between Santa Ysabel and Scissors Crossing. I decided to get to Scissors Crossing as quickly as I could, then go into "search" mode from there.

With the Beta NGS Map loaded on my phone and the phone mounted on the dash, I could easily spot potential recoveries along the way. It was still early and with little to no traffic on eastbound 78, I could slow down and scan for witness posts, concrete monuments, boulders, and obvious rock outcroppings without worrying about disrupting traffic; too, this area had plenty of space to pull off the road as needed.

BOR 20: AI4538 (GPSonBM, Secondary Mark)

When the world shut down last March due to the pandemic 🦠 I hit the desert for the beginning of an epic journey to hike 100 Peaks in San Diego County (completed in October 2020 😉), what better place to be when everyone was struggling with social distancing than solo hiking in the middle of the desert? AMIRIGHT?

One of my early Peaks on the Challenge last year was Grapevine Mountain. The trail started on the NOBO section of the Pacific Crest Trail (PCT) at Scissors Crossing then after two miles, I branched off from the PCT to continue on to Grapevine Mountain. Instead of doing a strict out-and-back, I headed over to bag Peak 3831, from there I spotted a faint use trail back to the road, ultimately popping out on the 78 about a half-mile east of where I'd parked the truck. Unbeknownst to me at the time, this marker was right across the street from where I left the trail! 🤣

Working the Line

If you've been following my survey mark hunting for any period of time, you may have recognized patterns in the numbering of some survey marks, this is most obvious with the U.S. Coast and Geodetic Survey (USC&GS) benchmarks that are often found very close to major roadways. The marks are part of individual surveying projects and generally, the numbering sequence increases as you move East to West, or South to North. The exact number of the series isn't that significant, it just has to be different from others in the region. For me, it's fun to see how many I can recover in a particular series.

Between Ramona and Westmoreland, traveling on SR 78, I've encountered three different series that are marked with USC&GS Benchmarks: 521, 580, and 579. I have previously recovered marks in each of these series.

  • Series 521 set in 1956 - Five previous recoveries

    • Four in the Santa Ysabel Quad: T 521, U 521, W 521, X 521

    • One in the Julian Quad: N 521

  • Series 580 set in 1939 - 4 previous recoveries

    • All the Julian Quad: M 580, S 580, T 580, U 580. It is interesting that while these marks are all dated 1939 they don't adhere to the expected E-W numbering schema. These four marks increment from West to East while today's recoveries in the 580 series incremented East to West 🤔

  • Series 579 set in1939 - 1 previous recovery

    • One recovered in the Borrego Mountain Quad: R 579

Note that the "Quad" reference above (ie. the Julian Quad) is to the USGS 7.5-minute Quadrangle Topo Map for the areas where the marks were located. A 7.5-minute quadrangle map can cover an area between 49 to 70 square miles. The image below shows the Quads for San Diego County.

USGS 7.5 Minute Quadrangles for San Diego County

580 Series Recoveries

Today I made five recoveries in the 580 series which included one that was obviously Lost/Destroyed. Many of these benchmarks are easy to find because they are right along the roadside and have visible witness posts nearby.

Once you get out into the desert, they can be even easier to spot because there are often fewer visual obstructions. Additionally, many of these marks are identified on the USGS Topo Maps with an "X" symbol, the letters "BM" and the recorded elevation for the marker. The newer NGS Beta Map includes an active GPS feature that helps locate marks in real-time. Even with printed GPS coordinates and a narrative description of how to reach a survey mark, you don't always find them, so the active GPS system is a big help. 👍🏻

To illustrate the map notations, I put together this graphic to show what I found (and didn't find) on a stretch of SR 78 in Sentenac Canyon, east of Scissors Crossing, and circled the appropriate symbols on the map. The driving distance between survey marks X 580 and H 480 was 1.77 miles.

I spent an hour recovering two survey marks in this section beginning from the time I parked to go look for X 580 to the time I hopped back in the truck after recovering H 580.

According to the datasheet, X 580 was 3.4-feet west of the witness post and was mounted on the top of a 4 x 5-foot granite boulder projecting about 1 foot above the ground. There clearly was not a granite boulder 3.4 feet west of the witness post as you can see in the picture, but what was exposed 1 foot above the ground in 1939, could very well be buried by now.

I kicked around in the dirt a little near the witness post, but I'd left my shovel in the car and didn't want to go back for it. 🤷🏻‍♂️ I spent about 20 minutes on this one alone, crashing around through the brush looking for a boulder that fit the description, working westward from the witness post, but was unsuccessful. The next time I'm out that way I will definitely bring a probe and shovel to do a more thorough search.

Normally I will go after all section corners that are close to the road, but I really didn't feel like climbing up this slope to recover this one, as you can see from the contours, it's moderately steep (each contour line = 40' of vertical gain, the closer the brown lines are together, the steeper the slope. VERY close lines means it's a cliff) Perhaps when I go back to dig around for X 580, I will go up and get this corner.

J 580 was an easy-peasy recovery in a rock outcropping right along the road, this was also a GPSonBM Secondary Mark.

L 521 was supposed to be mounted on the curb at the end of the San Felipe Creek bridge, but I couldn't find it. Armed with better information from the datasheet, I'll try again when I'm back out there.

The Gaging Station in the San Felipe Creek (under the bridge) is not a numbered survey point, but I thought it was pretty cool. Sometimes, gaging stations have survey marks or reference marks nearby; I looked but couldn't find any.

H 580 was also a GPSonBM Priority and an interesting find as it was on the roadside of the OLD road that went through here. I'll explain that a little more below with the individual pictures of that recovery.

J 580: DX0171 (GPSonBM, Secondary Mark)

As I mentioned above, this was a pretty easy find, I parked on the other side of the road directly across from the mark and it took me about 3 minutes to prep the mark, take the pictures and move on to the next one.

H 580: DX0168 (GPSonBM, 2 km, Priority B-2)

This was a cool recovery because it was on a rock outcropping that was next to the OLD bridge that went over San Felipe Creek! This mark, as all in this series, was set in 1939 and there have been some road realignments since then. The gallery above shows the position of the mark on the boulder in relation to the foundation for the old bridge. The gallery below provides a few other perspectives of the old road as well as the Gaging Station 👈🏻(click the link to learn more about gaging stations 🧠) that sits under the bridge, and the final picture is the view from the southwest end of the bridge, looking east.

For reference (and for those who may be spatially challenged 🙃) the picture of the old road (first image in this gallery) is on the north side (left) of the new bridge shown in the last image. 😉 I spent about a half-hour recovering this mark, exploring the old road and bridge footings, checking out the gaging station, and looking for potential survey marks related to the gaging station. As I mentioned earlier, I did a quick check for the L 521 marker that is SUPPOSED to be on the curb at the end of the bridge...but I didn't find it.

The REST of the 580s I found today (A - D)

These are presented in the gallery as I found them, heading east along SR 78 running along the dry creek bed of San Felipe Creek, in the southern foothills of Yaqui Ridge. D 580 was mounted in a boulder but the rest were set in concrete monuments. I found several survey marks today that still had reasonable remnants of the original 4"x 4" witness post with "U.S.B.M" carved out on them!

Unfortunately, A 580 has clearly been Lost/Destroyed, you can see where the entire top of the concrete monument has been broken off, survey mark and all! This is a good indication of how deep the monuments are set, due to erosion in the area of this mark you get a good cross-section of the monument column. Typically only about 6-inches of the monument would be above ground.

K 521: DX0369

The 521 series was set in 1956 and it was good to add another one to my list of recoveries for that series, hopefully, I'll be able to find L 521 on the bridge over San Felipe Creek next time I am out that way! Not only did this one have "USBM" painted in big yellow letters on the boulder, but there was also a traditional Witness Sign nearby.

Excavation Time!

Sometimes I really have to work for a recovery 🤷🏻‍♂️, and this was a good example of that. As I was driving down the road, I quickly located the witness stake for BOR 36, but I didn't see the monument anywhere around. I knew what I was looking for: a survey marker placed by the San Diego County Engineer Department in a concrete monument. These discs are distinctive, with a raised nipple in the center of the mark and the control point punched into the top of the nipple, the discs are often mounted on a steel rod driven into the ground until refusal and are surrounded by a concrete sleeve.

BOR 36: DX0371 (GPSonBM, Secondary Mark)

I knew this was the right spot for the marker based on the stamped aluminum tag on the witness stake (last image in the gallery) and based on the datasheet, I knew the mark was 1-foot west of the witness stake. When I arrived someone had kicked around the top of the berm next to the witness stake but they hadn't disturbed very much dirt, I grabbed my shovel and started digging. Worst case, I knew the mark would be flush with the ground (before the berm was built up) so I had to dig down a foot and a half to two feet to find it. My perseverance paid off and I got the recovery! 👏🏻🙃

579 Series Recoveries

This series was set in 1939 and logically preceded the 580 series. The entire series was set east to west and numbered A 579 through Z 579. I had previously recovered R 579 as a Drive-By Recovery on December 7, 2020, while I was en-route to hike Vallecitos Mountain High Point as part of the San Diego Sierra Club 100 Peak Challenge (it was peak #88/100, I still have 6 peaks left to go to finish that challenge) As I continued east on SR 78, I started recovering the 579 in descending order.

I revisited R 579 to grab an updated photo with the mark "chalked up" and to recover a nearby (literally across the road, see the second photo below) reference mark (R 579 RM 3), and an Azimuth Mark (S 579) that I was totally unaware of last December.

I edited the original recovery photos from December 2020 to add the recovery date, and on the eye-level photo, to show HOW FREAKING CLOSE THE REFERENCE MARK WAS! (that I didn't know about back then) 🤣😡🤷🏻‍♂️

The REST of the 579s I found today

Even though my recoveries were completed in descending order, I've presented them in this gallery in ascending order.

Today I found 15 new marks in this series to bring the series count up to 16 primary marks out of 26, plus the bonus Reference Mark for R 579. There were several of the remaining 10 that I couldn't find any evidence of whatsoever. In those cases, the expected location of the marks was in a graded road that parallels the 78 and is used for Off-Highway Vehicles (OHVs), it is very likely those marks have long since been lost or destroyed. There were a couple that was located in areas where it wasn't convenient to stop and look for them based on a variety of reasons.

(Note: my close-up photo of A 579 didn't come out, so I'm using an NGS file photo until I can get back out there and get a new picture, thankfully my eye-level photo was fine and I confirmed its latitude and longitude based on that.)

Other Cool Recoveries

California Division of Highways

Both of these survey markers set in 1963 were total surprises and lucky recoveries. AS 77 was in San Diego County while AS 93 was in Imperial County. When I stopped to recover U 579, I noticed another witness paddle nearby and was pleasantly surprised to make a bonus recovery. The double witness paddles on the side of the road marking AS 93 were a dead giveaway to some kind of survey mark, and it happened to be the same basic type as the previous recovery. I haven't dug into the respective County Surveyor's websites yet to locate the original survey(s) where these were set (and potentially find more related monuments), but that'll go on my "rainy day to-do list"

JT-HIWAY Monument

I am presuming this is an old Division of Highways monument, at first when I saw it from the road, I thought it was just another of the many "C" posts that mark the original Right-of-way for California highways. I've posted about those in the past, they are similar shaped concrete monuments with no more than 12" showing above ground and have a large "C" cast into the monument, the "C" faces the roadway. These were placed along California Highways at regular intervals and at the beginning, end, and apex of major curves in the road. When I slowed down to take a look at it, I could tell that it had more markings than a traditional "C" Post. Checking my map, it (coincidentally) was located close enough to a PLSS section corner, to make me think it was a fancy section corner, perhaps with the township and range etched into it. Upon closer inspection, it obviously was not a corner marker, and clearly had something to do with marking the highway.

I did some preliminary research and the best I could come up with was that the "JT-HIWAY" might refer to the old Julian Toll Road that ran between Julian and Brawley. The "DIST-110..." could refer to a distance such as a post-mile location. If the 110 did refer to mileage, it was on a version of the roadway that has since been straightened, rerouted, or shortened. Today, this marker sits at approximately post-mile 88 on SR 78 (based on its origination point in Oceanside and the current routing of the road). The marker could have been set in the early 1900s and it's conceivable that the route was back then was longer due to twists and turns, too there's always the issue of accuracy regarding measurements. Anyway, it's one I will continue to research because it's just kind of cool.

When I was processing all my photos, I noticed a similarly marked monument near the K 579 benchmark, the next time I'm out there, I may excavate around the front of each of these monuments in an effort to read the full markings on each. That may provide good information on their relationship and relative positions. I will also see what I can find out from Caltrans.

California Department of Transportation

Here are a couple of survey marks placed by the CA Department of Transportation, the first is near the intersection of SR 78 and 86. The mark also indicates that there is some overlap between 78 east and 86 south. I like how the witness paddle was stamped exactly as the survey marker was, nice touch!

The second mark was in a covered sleeve and is a High Precision Geodetic Network (HPGN-CA) Station, these are passive stations, brass or aluminum discs, that can be used as either primary control stations or as calibration points for Global National Satellite System (GNSS).

Obsidian Butte - The Main Event!

Thanks for hanging in with me to this point! 👍🏻 (If you used the quick link above to bypass the rest of this article, I encourage you to go back and read through it, there's some interesting info in here and it took me a long time to put it together!) 🤣

Obsidian Butte is one of five lava domes created by viscous lava rising in a volcanic vent and is one of the largest of the five buttes collectively known as the Salton Buttes.

The whole point of this trip was to visit Obsidian Butte, hike the rock pile, and look for the station disc at the top. A secondary agenda item (time permitting) was to visit the Sonny Bono Salton Sea National Wildlife Refuge. As things turned out, I spent WAY too much time looking for survey marks and didn't really have time to do the Wildlife Refuge 🙄 I was able to drive right up to the base of the butte and it was a short scramble up to the top. Despite not being very high (actual elevation: 150 feet BELOW Sea Level 🤣) the views were pretty amazing.

There was no survey mark at the summit, nor was there any evidence of the poured concrete monument, or two large boulders at the summit where the disc was supposed to be set as described in the datasheet. After walking around the top of the butte looking for the mark, I was a little puzzled by my elevation reading on my GAIA GPS.

I was at the high point based on the topo map, which was supposed to be 130 Feet Below Sea Level, but my GAIA had my elevation at 150 Feet Below Sea Level 🤔 The Butte had lost about 20-feet off the top!

Doing a bit of research, I found a paper titled: Age of Obsidian Butte in Imperial County, California, through infrared stimulated luminescence dating of Potassium Feldspar from tuffaceous sediment. (by Axel K. Schmitt, Andrew R. Perrine, Edward J. Rhodes, and Christian Fischer) where the authors note that "the central dome-like structure has been completely removed by quarrying..." If you are interested in Geology or Archeology, you may find this an interesting read.

The top of the butte provides some great views in all directions but is basically just a bunch of broken-up rock. However, once I started exploring the northeast side of the butte in search of a few other survey marks, the terrain was much more dramatic.

Understanding that these buttes are all volcanic formations certainly explains the cool rock formations that still exist on this northeast side. Much of the front and top of the butte shows the effects of quarrying activity over the years...on my initial approach, it looked very much like just a big pile of rocks.

The Final Recoveries of the Day!

It had been a long day, and I knew that I had a solid 2-hour drive ahead of me to get home. My NGS Beta Map showed that in addition to the OBSIDIAN mark, there were three other survey marks located on/around the butte. I was able to recover two of them, both were also GPS on Bench Marks targets, so that was a good thing!

S 1246: DW0217 (GPSonBM, Secondary Mark)