Could someone please tell me where I could find an elevation for this benchmark? I will not be using it. Just curious. I ran across it doing a topo. It is located in central Iowa.
Thanks!
I looked for a datasheet for it, but could not find one.
Probably in the archives. Needs an extended search. Guaranteed to be there somewhere.
Cliff, do you see any reason to stick a PK in a BM???
It looks like a temporary bench mark, as might be used when transferring the elevation from a mark to be reset. There may not have any published data associated with it.
Beats me.
I'm curious to know more about the location. The 3-76 suggests Allamakee county, which of course is not in central Iowa, so I'm stumped there.
I've seen a few hundred C&GS marks and never run into one of these. I like the idea that it was a TBM for a reset, or else that it could be just a "shiner" used as a reference tie.
How far was it from the nearest mark found in the NGS data base?
Story County
The three next closest marks are roughly 330', 2700', and 4,400'.
If that's a nail inside a washer in a concrete cylinder, then it is probably an azimuth mark to the BM 330' away.
Bruce
Please provide some more specific information about the location of this mark. This was a temp style mark (obviously it has done it's job) and I may be able to track it down in the field abstract for the level line when it was set.
It is a pk nail in a washer in the concrete floor at the center of a hangar door at the airport. I found another one at the corner of the terminal building.
Don't you think providing the name of the airport or a Lat/Lon for this monument might help someone assist you?
Howdy,
I am almost sure (95%) of the following:
Since the point is located on an airport and has a copper washer with USC&GS stamped in it, it was established as part of the Airport Obstruction Chart program. This program began in 1948 and was/is an interagency cooperative effort with the FAA. The "client" was the FAA; data was provided to them. The AOC program was absorbed into the NGS in about 1994. The tie to the vertical network was no better than third-order.
Prior to the absorption of the AOC program, accuracy standards were determined by the FAA and NOAA Photogrammetry Division. The heights were intended to support the obstruction chart items as well as providing heights for runways, instrument landing system components and related items.
The leveling records were NOT submitted for inclusion into the NGS data base. They are most likely not available in digital form.
P.K. nails and copper (and later aluminum) washers were never intended as "permanent" monumentation. You can probably find similar "monuments" at the airport's runway ends.
If you want to find some non-verifiable values for these points, contact the NGS Field Operations Branch in Norfolk, Va. You should provide them the name of the airport, the stamping of the washer and hope the data is still available.
Good luck,
DMM
I researched all the level lines we have in the National Spatial Reference System in the county. Regrettably, I didn't find any evidence of this mark and the other one you referenced, however I did find notations about temp. BMs designated as "77" 1,2,3, etc. Unfortunately the master listings don't provide the descriptions of the marks, but these nail/washers were pretty typical of the temp points C&GS used. The marks designated 77 were set as temps during some leveling by the Iowa Geodetic Survey, which was part of the Civil Works Administration (CWA) programs of the mid-1930s. While these efforts typically used USC&GS and State Survey disks and the USC&GS nail/washer temp points the vast majority of the data was never completed and submitted to C&GS for inclusion in the national networks. I suspect that these marks were part of one of those lines for which the data never came back to us.