Buried surface mark or underground mark?

[+Rotareneg]

Spent an afternoon driving around looking for graves with my mom (for findagrave.com) and picking off the odd benchmark here and there. The last one we found was KG0551, PHILLAIRPORT. It was under the bottom of a roughly two foot deep hole in the bottom of a ditch, which is making me wonder if it's actually the surface mark or if that's gone and the mark we found was an underground mark. The depth on the data sheet has changed from flush when monumented in '50 to 4" in '85. Also, all the other 1950 marks I've found in the area have at least a mild patina, this one is very shiny and has almost no patina.

 

Here are some larger photos:

 

 

 

[Bill93]

Sounds like it is well could be the UG mark. What is your judgment about the ground having been filled versus a ditch being cut?

 

You could take a long probe and see if there was a concrete post under it like the top mark would have, or just a small lump of concrete which was typically poured into the post hole for the UG disk. Be careful not to dislodge the disk if its concrete is small.

 

Another clue would be if there is tar residue, like an old asphalt shingle, on the disk or post, which was used to separate the lower and upper pieces of concrete.

[kayakbird]

I don't see anything in the original description that indicates that underground marks were set. Is there a nearby BM that a quick level run could tie to? kayakbird

[Bill93]

I think for a long time they usually set underground marks that were not always noted on the data sheet just because it was so common.

 

Good catch on the elevation. I didn't think to check whether a tri-station had good elevation, since so many do not.

 

RM3 has a good elevation that could be used if he gets permission to go there and is able to find it. At 202.45 ft distance you might be able to do it with a handyman laser level when daylight is dim.

 

The next one listed on GC is 0.3 mile away, which would require decent gear and several setups. But how many people posting here are equipped to do a level run? I think maybe you said you were, and I've done it, and we occasionally hear from a pro, but anybody else?

Edited September 27, 2010 by Bill93

[+Rotareneg]

I'll go back up there some time with a couple of yard sticks and use my camera and a bubble level to do a rough leveling with RM 3. There are some newer looking sewer covers in the ditch, so it's quite possible the ditch has been worked on.

 

The Google street view shows the ditch and the hangar in the background where RM 3 is.

[2oldfarts (the rockhounders)]

I think it has been mentioned that most underground marks are set in a 'mass' of concrete and not normally in a square or round post.

 

I would check the concrete the mark is in and see if it is a square post 10" in diameter. If not, then you have found the underground mark.

 

John

[+Rotareneg]

I'll try that first. Didn't want to submit a recovery to the NGS without knowing for sure.

[mloser]

Google Earth shows a manhole cover that seems to about where the mark was. Do you think they built up the ground and put the cover over it, and subsequent work removed that cover? Or am I looking at a totally wrong spot?

[NGS Surveyor]

See page 92 of http://docs.lib.noaa.gov/rescue/cgs_specpu...35no2471950.pdf for a cross-section drawing of a concrete mark and an underground mark. Note, the date of this pub. is 1950. Also note that the drawing shows sand and a board separating the UG mark and the surface mark. Both disks should have been stamped the same and both should have been Triangulation Station disks. Hope this helps.

 

GeorgeL

NGS

[NGS Surveyor]

See page 92 of http://docs.lib.noaa.gov/rescue/cgs_specpu...35no2471950.pdf for a cross-section drawing of a concrete mark and an underground mark. Note, the date of this pub. is 1950. Also note that the drawing shows sand and a board separating the UG mark and the surface mark. Both disks should have been stamped the same and both should have been Triangulation Station disks. Hope this helps.

 

GeorgeL

NGS

[+Rotareneg]

Google Earth shows a manhole cover that seems to about where the mark was. Do you think they built up the ground and put the cover over it, and subsequent work removed that cover? Or am I looking at a totally wrong spot?

 

It's about halfway between that cover and the culvert under the road, right in the lowest part of the ditch.

[+Rotareneg]

Went back out there this afternoon, and yep, it's set in a rough lump of concrete instead of the normal smooth topped post. It was also clearly multiple feet below RM 3 instead of just half an inch lowers as the datasheets would indicate.

[kayakbird]

Rotareneg, Thanks for the follow up. Always nice to hear the rest of the story. kayakbird

[kayakbird]

Rotareneg, Thanks for the follow up. Always nice to hear the rest of the story. kayakbird