Construction Of A Benchmark

[Photobuff]

There is a particular 1942 benchmark I've been looking for, as it's close to home and has no recovery info since it was monumented. I tried looking by coordinates, but no joy there. I then very carefully followed the directions from a nearby town, and was surprised and amazed to find that the directions brought me right to the front of my house! None of the original landmarks still exist, but I did find a strange cement patch in the front yard of my neighbor across the street, about where I think the benchmark might have been. Thus, in roundabout fashion, my question. When benchmarks were set in the top of a square cement post, did they just sink a uniform post, or did they pour concrete in a hole and mold the top into the post? The patch of concrete is irregular, and doesn't show any evidence of surrounding any type of secondary cement post. Also, what does the bottom of a benchmark look like? Has it got some sort of protrusion that goes deep in the concrete? Is there any way I can determine with certainty if this cement patch is the remains of what I'm looking for?

[DaveD]

While marks come in numerous shapes and sizes, in general, the NGS/C&GS mark setter would dig a hole approximately 4 1/2 feet deep which would be belled at the bottom to limit motion. The hole would be approximately 14" in diameter and filled with concrete. If the surface mark were to be above ground it would be molded with a wooden form and carefully smoothed on top where the disk would be placed. Even if mark was set at or below ground level then the surface would be trowled smooth before the mark was inserted into the concrete. If the mark was also a triangulation station then there would have been an underground mark plumbed directly beneath the surface mark in the concrete in the base of the hole which would then be covered by some light wood and sand before the rest of the hole was filled with concrete. This would ensure that if the surface mark was disturbed or destroyed that the high accuracy horizontal position would be maintained by the underground mark. If the surface mark was set just for vertical purposes then an underground mark was not necessary.

[Bill93]

Post out of ground in this picture seems to be typical--I've seen another destroyed one also that was a twin except its hole had been better shaped. Interestingly, these weren't anywhere near 4 1/2 feet even if they were set flush, which this one probably was not. Edited November 17, 2005 by Bill93

[Photobuff]

Wow, this is looking more interesting. The irregular cement patch is the right size according to the photos posted. The published coordinates on this one are way off, almost a mile up the road. That's why I was so surprised to find the verbal directions put it right at home. The verbal directions to markers further up the road appear to be spot on (and their coordinates stink as well), so this is likely the same situation. There is another clue I have to investigate. This road is a fairly steep hill. The elevation of the marker will locate it to a very narrow area. Even though the lat/long were off, I assume the adjusted vertical will be very good. My GPSr won't be nearlyl as good, but under the right conditions it should put me on the right lot. Finally, that property was in the same local family since the 1800s. Unfortuantely, the man who'd know passed on a couple years ago, and his wife moved to Florida. If I can get hold of her, she might easily know the history. Who knows, maybe she's got the disk ;-)

 

Thanks all- what a great crew this is!

[+Sagefox]

Check the photo for this benchmark to see what the underside of a disk looks like.

 

Benchmark "Sugar"

 

Check out the view photos also. Its great when you can benchmark and get great views.

Edited November 17, 2005 by Team Sagefox

[+Spoo]

Try this for an underside view:

 

Underside view

 

This is one photo from my sequence, My Very Own Monument taken last August.

 

Unfortunately, my monument is drilled in bedrock, not cast in a concrete post.

[+W4G_SOTAGoat]

I found what appears to be a benchmark that was filled in over, but they placed a pipe down so you could still access it. The pipe coordinates were dead on with what the USGS has in their datasheet.

 

http://www.geocaching.com/mark/details.aspx?PID=AB4259

Edited November 17, 2005 by Clayshooter

[mloser]

I have run across a couple "types" of concrete monuments.

Here is the massive type at Ridgeview, Harrisburg, PA and a Reference Mark for Ridgeview.

Both were pushed into the woods from where they belonged, most likely by whoever graded a hill behind a movie theater and put in water lines.

 

More likely though, your 1942 mark is a precast post--all the 1942 marks in my area are. Here is KW1117. Look at the pictures taken by Airnut to get an idea what the post looks like. I am not sure how long these posts are, but I have come to the conclusion that they are a failure, especially when allowed to stick out of the ground more than a few inches. They are very prone to any strike and simply crack off. I think I have found at least 5 of these destroyed.

 

Chapter 42, Appendix D, in NOAA Manual NOS NGS 1 describes the precast posts a bit.

 

Team Sagefox's pic of a benchmark from the side is typical. The tabs at the bottom are often spread when imbedded in concrete, making it less likely to come out or be pulled out.

 

Edit: I just checked your recoveries. The mark should be exactly like NB0909 if that one is also close to you. If you see a square top like this then you are looking for a precast post like I described earlier in this post.

 

Matt

Edited November 17, 2005 by mloser

[Photobuff]

Thanks all- here's the latest. This morning I walked down the hill to the lake, the elevation of which is controlled and known accurately. I was able to measure it to within a couple feet when the GSP signals were good. Then I walked up the hill and checked the cement patch across the street. No good. The elevation is too low. I headed up the hill. There are several possibilities, but the road flattens out, thus the uncertainty increases. In one place, there are now lawns and driveways, so the mark might have been buried, paved over, or just broken off. There is another spot with a couple pieces of red survey tape on a tree branch, some quite old and some quite new, and a depression I didn't have the tools to investigate properly. The ground is built up there, so the mark would be below the surface if it still exists. I wonder if there are benchmarks the local surveyors know about, that don't show any recovery info? Just how they'd know is beyond me, as neither the coordinates or the verbal directions are sufficient to find the thing. Next trip I'll bring a piece of stiff welding rod and poke around a bit. All suggestions regarding "tricks of the trade" happily accepted

[mloser]

Your idea of a wire is a good one. Most of us use some sort of probe. Mine is a Walmart camp fork with the fork part removed. It gives me a wooden handle on the end of a metal probe about 30 inches long. I have a permanant callous in the center of my right hand from using it. Others use long screwdrivers and homemade probes. They are indispensible! Even if the mark is not listed as being underground it may be covered by leaves and dirt. It is simple to tell concrete from soft ground but some of us can tell the differnce between concrete monuments and smaller rocks by the sound, and I know of one person here who claims he can tell the sound of the actual disk from the monument. I would guess that the probe has helped me find about 20 percent of all the marks I have found, and 90 percent of the ones that were actually underground.

 

A metal detector can be handy, but I rarely use mine. So far I have found one disk with it, out of about 50 searched for. I get it out only when the frustration level is high. It is not good for general sweeping of the ground as in searching for coins on the beach or claymores in a minefield. It is more of a pinpointer when I know the general area and suspect the disk is under dirt, moss, etc. It has proven its value when searching for disks set on boulders, since probing there turns up just hard objects (no, I cannot tell by the clink if it is bronze or stone).

 

Compass. Not the one in your GPSr, even if it has a magnetic compass built in. Nothing takes the place of a decent handheld compass. I use my GPSr compass for rough estimates but when it comes time to find reference marks of a triangulation station I whip out the ol' needle. Take the declination into account there though. When using compass directions, bear in mind that if they say something is NW of a power pole, they mean roughly NW, but definitely NOT North or WNW. Those directions would have been used if appropriate.

 

100 foot measuring tape. Any shorter and you will be hard pressed to measure any distances with accuracy. Any longer and it will be a pain to carry. When I am in doubt about a disks location from a reference point, I run out the tape, and then use it to swing part of an arc while I probe at the specified distance. You can't do that if the tape doesn't run the whole distance.

 

USAPhotoMaps is my armchair tool. I almost always look at it to see what I am hunting for, usually casually, but if there is a tough mark I return to it to study the landscape on both the topo and aerial photo of the location. Often it can turn up missing references, such as abandoned or moved roads, old building sites, etc.

 

A shovel is often necessary. I have a (now broken) camp shovel that folds to fit into a backpack, but most people carry a trowel of some sort. I once carried a full size shovel to a location I had searched 3 times before to more efficiently dig out a mark, which turned out to be just the stem.

 

Yes there are marks that are not in the NGS database. Many marks are controlled by states and counties and their appropriate agencies have the information on them, usually in paper form (the USGS has thousands of survey marks in their paper files. Some here hunt them but I have enough to hunt for with NGS marks). The survey tapes are not insignificant. There is a survey marker nearby. It could be anything from a property corner (not likely if there are multiple tapes, and they are in a tree.) to a county marker, to the station you are hunting. The mark will be on the side of the tree with the tapes and probably won't be too far from it. Your probe may help you there if there is a depression. I have poked my fingers through the grass in such likely spots and turned up benchmarks, after hitting something hard with the probe of course. I don't go randomly poking my fingers in lawns.

 

I have only heard of marks that were off the published coords by as much as you describe, and never located on myself. I would be suspicious of that. You can expect the coordinates to be off by 50 or so feet, and they are sometimes off by 200 or so (and up to 600, I have heard), but a mile means something major is amiss. This is where knowledge of the local area helps you tell which is right and which is wrong.

 

What mark are you searching for?

[+W4G_SOTAGoat]

The published coordinates for DG0405 is about 180' off. I went to look for it after work today and had to use the textual information to find it.

[mloser]

For scaled marks I only use the GPSr to get me to the benchmark location, especially now that I have to stray farther from home to get to ones I haven't recovered. Once there I take out the description and go by it.

[Photobuff]

My road has a series of benchmarks, all measured from a town just under five miles away. Today I decided to check the distance not from the town, but from the nearest benchmark. I'm now convinced that the description, coordinates, and landmarks all agree. Unfortunately, the major landmark, a barn, is now a pile of rubble, and I'll have to see if I can figure out where the corner was. It should now be a matter of poking around and maybe using a metal detector (I heard Harbor Freight has one for $24.95). Thanks for the tip on the Microsoft terrathingie- that's way better than the maps I've got.

 

Today I looked for another MIA benchmark, one in Victor NY. Didn't find it either, but all the landmarks are still present. What I did find was a shallow hole right about where I think the mark should be. It wasn't deep enough to have held the entire thing, so I think somebody took a guess and missed. This one will be harder to poke around for, as the area is thick with construction debris in the form of pieces of concrete, along with a huge amount of shale and various pieces of metal.

 

Yet another question- what kind of metal are the benchmarks made out of? That has some ramifications as far as the metal detector is concerned.

 

Why is this so addictive?

[2oldfarts (the rockhounders)]

Photobuff,

 

If you can find just one of the benchmarks that are measured from your town then you can use it to figure out how far each mark is from it.

 

Most benchmark are of a brass/bronze alloy.

 

Good hunting,

 

John

[+Harry Dolphin]

And sometimes, the coordinates are terribly wrong. Perhaps, moreso with older intersection stations. Two in Union City, NJ were found/not found by the description. The coords were .40 mile off. I am going to have to call in a political favor to search for Rockaway. Coords are a full minute off, I think. And now inside a building.

I definitely need to bring a probe and gardening trowel with me. We think we found the location of a disk in a sidewalk in Newark, but the cover was missing, and hole was filled with dirt. We didn't have anything to dig with. Oh, well.

[Photobuff]

FWIW, we have a Harbor Freight store in nearby Rochester NY. Just as a friend told me, they have metal detectors for the princely sum of around $26. Construction is "economy", but it can detect ferrous metals with a null, and non-ferrous metals with a beep. Has two tuning controls and volume. Seems quite sensitive. If, like me, it's not your main interest, but you want to have something available, this seems to fit the bill.

[+seventhings]

Harry's right - sometimes the location of marks with SCALED coordinates can be WAY off.

 

One day, I went in search of KV0202 at St. James' Church at the corner of Amboy Ave and Grove STREET in Woodbridge, NJ. Normally, I would not use my GPS to find a mark with SCALED coordinates. But the church was rebuilt after the last description so, to get another level of confidence that the mark was destroyed, I plugged in the coordinates and hit GOTO. The GOTO indicated that the mark was 0.5 miles north. I wondered, could there be another St. James Church? So I drove north along Amboy Ave until the GOTO said 0.0. And there I was, at the corner of Amboy Ave and Grove AVENUE. And that's how this sort of thing can happen: the "scaler" was working off a topo with street names and fixed the wrong Grove.

 

0.5 miles is the worst "miss" that I've seen. Typically, the coordinates for marks with SCALED coordinates are 100-150 feet from actual.

 

When searching for marks with SCALED coordinates, the GPS' GOTO is good for telling you when you should start looking for a place to park. The written description is only way to find such marks reliably.

 

Will

[Photobuff]

Ok gang, I'm tickled to death. This morning I went out with the right tools- GPSr, compass, metal detector, and short handled straight ended spade tool ($9 at Harbor Freight), and recovered three benchmarks! One of them was the one just up the road that I've been fretting over for some days now (NB0908). In every single case, the benchmarks were buried, and finding them without the metal detector would have been near impossible. Even the "easy" one in a drain culvert was easier with the detector, as it was well buried and blended in with the surface. Unfortunately, we're expecting snow soon, and this doesn't seem like a good winter hobby

 

At any rate, this is about the best fun one can have on a nice fall day!

[2oldfarts (the rockhounders)]

Unfortunately, we're expecting snow soon, and this doesn't seem like a good winter hobby 

 

At any rate, this is about the best fun one can have on a nice fall day!

 

When the snow is covering the ground there is always the intersection type of benchmarks. The steeples, towers, lighthouses, etc.

 

Have fun,

 

John