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What Is This?


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While hunting this mark, we ran into this:





Any idea what this is? We haven't seen one of these before.


edit: I guess I should explain a bit more. The first pic shows a rod in the center of the hole. The hole was around 8 inches deep, and the rod was about 4 inches tall. There didn't seem to be any distinguishing features of or on the rod. In fact, it reminded us of a piece of 3/4" rebar.

Edited by CacheCreatures
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I checked it out. They look very simular, but with the other post's pic it is clear that it is a vertical control mark and a part of the National Geodetic Survey. The one we found doesn't have any of that type of info. That is what has us confused. We are curious what the heck this really is. :P


The only info I have found is that "Brainard Kilman" is a company related to soil, water, and all types of geological /geotechnical testing.

If anyone knows more we are interested.

Edited by CacheCreatures
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Using a steel or copper coated rod for a vertical benchmark is a common practice in the surveying community. Many of the benchmark hunters in this forum have found them, although most have not realized it. On the older marks of this type, a standard brassdisk (the type we're all used to finding) was placed on the top, and the rod was not seen. In more recent years, the rods have begun to remain uncapped and the top of the rod is the mark. This is to allow a more precise horizontal position of the mark.


CacheCreatures, the mark that you found is most likely a piece of rebar, like you suggested. As a matter of fact, I commonly use 5/8" rebar as temporary vertical control on many of my jobsites. My temporary control is not set in anything as permanent as a capped well, however. It's usually just down in a hole about 6"-8" deep with lath and flagging around it.


It looks as though the mark that you found was for elevation monitoring. In my area (central to west Fresno County, Calif.) there are areas that are very susceptable to subsidence due to the pumping of water from the underground aquifers. Pump the water out and the ground elevation falls, like deflating a balloon. This can be of particular concern to farmers and irrigation districts whose canals and pipelines are designed to be gravity fed and/or zero-slope. Monitoring stations like this are usually checked seasonally, but sometimes more if necessary.


In your area I would imagine that the ground movement would be more susceptable the tectonic activity than that of the underground water tables. Either way, the monitoring station serves the same purpose.

Edited by Kewaneh & Shark
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Very interesting! So, is this, not the disk seen in our log pic, the actual mark HT3818 is referring too? Or, perhaps, are you suggesting this is a very old mark that was replaced by HT3818, but not removed for some reason (and there is no catalog record for it)? Or, rather, are you suggesting this is a completely separate mark located only a few feet away from a USGS disk, used for different reasons altogether (maybe a private company/land owner?)


We ran into a situation like the middle question just yesterday. We found HS3917 right where the description said it should be. However, as we were leaving we basically tripped over another disk with the same designation 50 feet away, marked "Reset". Our guess is this mark was to replace the original disk, and the original disk wasn't removed because it was expected to be destroyed during the as of yet not started road construction (expansion).


Is this a fairly common practice? That is, is it typical to replace/reposition a mark and leave the other behind, assuming it will be destroyed either through neglect or construction?

Edited by CacheCreatures
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The picture (logged on the benchmark page) of the disk on the bridge is the benchmark noted in the description. The rod in the encasing pipe would be to keep tabs on the bridge movements as refered to by Kewaneh & Shark (who is in the surveying profession). For more info on this unuaual rod contact Brainard Kilman.


As to the reset question we best let one of the surveyors answer for a correct response. Trust Kewaneh & Shark, El Camino, Dave D, or one of the other surveyors, who tolerate us amatuers!


John & Shirley

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That could be a property corner, plat corner, section corner or road alignment point. Looks like its been there for many years. May have nothing to do with a benchmark.




When taking photos of marks, its a good idea to take a photo of the area with the object in question marked. They puts the mark in context to the surroundings.


We use cast iron monument box's and rods very similar to these monument highway alignment control and or any property corners that fell within the pavement.

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The brassdisk in the picture of HT3818 looks like the correct mark. It is described as a disk in a concrete slab less than a foot from a wall and a paving notch (a change in the pavement surface). The mark shown is all that. The rod in the well may or may not have any relation to the disk. Both theories by 2OldFarts and ElCamino are very possible. It is difficult to tell from the pictures posted of the rebar in the well where it is in relation to the bridge or the mark on the bridge. I'll second ElCamino by saying that pictures of the surrounding area would be helpful.


The first picture shown for HS3917 is the described mark. I base that on the mark's relation to the end of the concrete head wall (as seen to the left of the mark and PDA). Why the mark was 'reset' before it ever removed in the first place is anyone's guess, but the possibility of future construction might be correct. Because the reset mark is in a different location (you say about 50 feet away) it would need to be blue-booked into the NGS database seperately from the original mark (as all reset marks should).


It is common practice in surveying to replace survey marks, but it is usually done after any construction is completed. Prior to construction, multiple 'swing-ties' are made to the mark in question, then when construction is complete, the ties are used to re-establish the location of the mark. If the reset is placed prior to the completion, it could get removed as well.

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Ditto the "intrigue" and "education" parts! My dad was an architect, and I ran across the occasional survey disk when I tagged along with him. Since GC added the benchmarking section, I've gotten as much, sometimes more, enjoyment out of hunting suvey markers as I do solving puzzle caches. The really neat thing is being able to take a 30-50-80-year-old Description and find the mark, despite all the changes that might have occurred in the area.


Thanks for sharing that Brainard Kilman thing with us :blink:

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Right on the money Chaosmanor! Although I don't have many finds yet it is partly the detective work necessary that gets me excited about benchmarking. Even when I think I know an area well I will still have to look for evidence of something that used to exist and no longer does, at least as descripbed in 1942, or 1966, or whatever.


C'mon snow. MELT!

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