m&h

Briefly, the marks were set either as horizontal control marks or elevation control marks. In the profession, the latter are the only ones correctly denoted by the term "bench mark." Bench marks were set during leveling runs, in which crews working with vertical measuring rods and leveling telescopes measured heights, starting at known points. Horizontal control, until GPS came along, was done by triangulation--trigonometric measurement of triangles, using a theodolite, with marks set at the corners, starting from baselines measured with extraordinary precision. Triangulation involved sighting over much greater distances than are typical with leveling, so the effects of atmospheric and meteorological distortions could be minimized by working at night. Crews included light keepers, who went to specified points and turned on their lamps at appointed times. The lamps and the instruments were usually mounted on tripods, centered with great care above the points, and their height above the points measured and recorded. "Height of light above station was 1.66 meters." This is very cursory. Much more detail is available in downloadable NGS publications put out over the past hundred years. See http://docs.lib.noaa.gov/rescue/cgs_specpu...s_specpubs.html.

Every month, it seems, we figure out a little bit more about how to look over these data. As always, we thank you for all you do. Cheers,

Fabulous find! We're as mystified as anyone at the discrepancies, though we see a possible transposition in 8.650 and 8.56. It's also interesting to come upon those 1927 azimuths taken from the south through west; this used to be done more often, but NGS policy seems to be to convert them, when they appear, to azimuths from north for the box score. Mainly, though, congratulations!

Yes, a level bridge! Although there is usually a close correlation between a mark's designation and the name stamped on it, there are marks whose stamping does not much resemble the designation. The data sheet provides both, so identification of a mark by what is stamped on it can usually be managed by anyone in possession of the data sheet. Before GPS came along, surveyors looking for the marks used to go pretty much by the written descriptions, and still rely heavily on them. In any case the coordinates for these two marks are scaled, so they may not be all that close. Cheers,

Hi, Dixiedawn, Our thought about the stampings on these two disks is that both represent the elevation as originally calculated in feet. The data sheet says the heights were adjusted in 1991, and the current heights are a little less than two feet more than the stampings. Interesting that the adjusted heights differ by a single hundredth of a foot. Because the designations are the originally-calculated heights, they left the A off to prevent a kind of confusion that seemed more important than the kind they left behind. That's our guess, anyway. Cheers,

We were in South Tacoma on an errand a couple of days ago, and decided to look for SY0664 STA 20 USAF, which has been logged here several times, and which seemed interesting because its elevation had apparently been changed, some time between its setting and its first recovery (the years for which are switched on the data sheet.) Taping our way to the point, we arrived at a broken stem and some concrete fragments, so we reported the mark destroyed. This morning we thought of comparing our photo of a couple of fragments with an excellent picture of the mark in cachelizard's immediately preceding log, and we found a point of correspondence. We wish the mark hadn't been destroyed, but we felt lucky to land this extra bit of evidence. Incidentally, we doubt that the existence of the broken stem entitles this mark to a "poor" rating, because it is an elevation mark, and the original height cannot be usefully estimated from what remains. Maybe it could in rare cases, for example if the remains were a strong pipe to which a standard disk had been brazed. But on this particular point, elevation matters already seem weird enough. Cheers,

Our latest good day hunting started Sunday and finished up Tuesday, on a mark we've been thinking about for several months, because it presented some challenges of access. It's SY2334, CLARK POT, in Tacoma, WA. When we logged it, we found ourselves preceded on both sites by people who had looked at the site from outside the fence and gone away. As we did, some time back.

As always, we're grateful. We have a fine time nosing around the list and the maps. Many, many thanks.

Our relatively slow pace of searching and recovering has so far meant that we haven't felt the need of programs like GSAK, but we do find it useful to have fairly accurate drawings when there's a main mark with some reference objects. We use an elementary survey platting program called Plat Pronto. A short steep learning curve, but useful results. We don't know of any way to overlay the drawings, though. We also fairly habitually run the old NGS program FORWARD.EXE between the main mark and each of the reference objects, to get separate sets of coordinates. These are very rarely useful on the ground, being too close together, but plugged in to Google Earth they can give a helpful picture of the layout. Cheers,

George-- A fabulous job-- just superb. It's easy to see that we'll reread it every now and again; it's not only interesting, but tremendously useful. Many thanks! Cheers.

Hi, John-- Can't help with the setting puzzle, but maybe the east-west road is 389, for which 89 is a typo. Some maps give Pratt Street that three-digit number. Good luck! It'll be a while yet before we're back in Arizona. Cheers,

Some time back we read the document on the ten-year plan, and so came to understand the diminishing importance of passive horizontal control marks. We still have some partiality to triangulation stations, just because it’s interesting to see whether the reference marks and the azimuth marks are discoverable. As long as the people in charge of the NGS database are willing to receive reports on them, we’ll send them, along with whatever elevation marks we find, knowing that they tend to have more usefulness. More recently, we were among the participants in a discussion here about whether it was a good idea to reset loose disks. Our position then was pretty much in line with that maintained by NGS for many years: don’t do it. Plenty of excellent reasons. However, in the case of this mark in Idaho, it seems plausible that a professional could re-set the destroyed RM, in its original position within acceptable tolerances, and describe this resetting in a recovery note. The integrity of the main station remains as it has, and NGS isn’t going to be checking up on it. (This provided that there is somebody who wants to pay for the job.) It seems that these stations are gradually evolving into museum pieces or archeological sites, so a little careful maintenance now seems less intrusive than it might once have done. Some portion of our blood is being thoroughly curdled by this suggestion, of course; it sounds like the ravings of an anarchist. Nevertheless . . . Cheers,

George-- Yes, we had a moment of excitement over a 1971 stamping, but it was a USC&GS disk. Good luck. Cheers,

We’re grateful to the Tillamurphs for the compliment, but such knowledge as we possess won’t add much to what has already been said. We have not seen the concrete marker in the courtyard of the Governor’s Palace, if by “courtyard” you mean the area north of the building with several trees growing in it. Your phrase ending with the question mark, “first benchmark,” is not easy to understand. Do you mean you have seen or read something somewhere that might suggest that this concrete marker is a first benchmark -- ever? In New Mexico? In Santa Fe? Your item #2 is also unknown to us. It sounds like a disk, in which case it is one of the thousands not included in the NGS or GC.com databases. We don’t do Waymarking ourselves, though we do keep in our own records interesting non-NGS marks that we’ve turned up here and there. It’s kind of funny, but true: you really don’t need a GPS receiver to find a mark, but it’s tough to find documentation of a mark without having its coordinates. Haffy’s suggestion, to use Google Earth, is excellent if you haven’t taken coordinates yourself. Once you have those, as earlier posters have said, you can enter them in search windows at GC.com or NGS and find what’s within a specified radius. If what you’re looking at isn’t NGS, it’s sometimes fun to track down the agency that is responsible for it--city, county, USGS, Corps of Engineers, National Ocean Service, etc. Sometimes not so fun, too, if all you’ve found is a property corner. Good hunting! We see that you’re no stranger to geocaching, so whatever looks hard to you now ought to look easier pretty quickly. Cheers,

MR. JOMG-- John's advice is excellent. We would add that if you haven't, you should read the FAQ on the main page of the Benchmarking site, especially the sections concerned with logging marks and with common errors in logging marks. A mark is destroyed only if you can prove that it is no longer at the position where it was set. So if a sidewalk has been poured over the spot where the marker was, the marker is in a sense "gone," because it can't be seen or used in any way by surveyors. But it isn't destroyed if the concrete was simply poured over it. Most of the time it is very hard to prove whether the mark is or isn't under the concrete. So, as John says, you need to be able to demonstrate with photographs that the present bridge's abutments are not the same ones that supported the earlier bridge. If the old abutments are there and have been used in such a way as to cover up the place where the mark was, then it might still (quite uselessly) be there. In such cases the correct recovery phrase is "not found," with explanation. However, if you can find pictures of the old bridge, or detailed newspaper reports of the extent of its destruction, and can put together a report that proves the mark has been removed from the place where it was set, then you can send it by e-mail to Deb.Brown@noaa.gov. What you submit should amount to proof, rather than powerful suggestion or persuasive indication or highly suggestive findings. Cheers,

As always, our amazed gratitude! Cheers,

We can't speak to the question of the differences. The closest we've come to geocaching was some months back when we joined in an online resection challenge posed by Klemmer and TeddyBearMama. We started hunting survey marks about four years ago, and have yet to even see a cache. Cheers,

Thanks, George! Cheers,

Fascinating find(s)! Our guesses on questions 1, 3, and 4 are 1. Pretty scarce, we'd suppose; we've never seen an instance of a disk specifically set as an azimuth mark and given a reference mark. Obviously, there are many instances of sets of triangulation stations, each with two RMS, where the two main stations are each other's azimuth marks. That's something else. 3. We imagine that the USACE disk was there already when the azimuth mark was set, and so came in handy as a reference, and 4. could only be marked by hand in the field. Great log! Cheers,

These vertical marks were set during leveling runs, and mark precise elevation. It is possible to place a knife blade, or even a machete blade, into the horizontal tick mark on the disk in such a way as to be able to place a leveling rod on the side of the blade. This does not usually make for the greatest accuracy. The mark may also be observed directly from a level set up so that its instrument height is zero relative to the disk. There are also leveling tapes available for this precise purpose, held against the wall with an index mark at the disk's tick mark, and checked for verticality with the vertical hair of the level scope. We have seen USC&GS descriptions of some of these procedures, and thought to look them up for this reply, but haven't found them yet. Fortunately, instruments don't have to be set up "over" these marks. Cheers.

Further apologetics. We'd like to know what the USGS county lists are. You've clearly found enough marks to avoid the confusion we mentioned above. Sorry. Cheers,

As we read over your post again, we wonder whether (a) there is a USGS county list that we've never heard of, or ( you may be confusing the USGS (United States Geological Survey) with NGS (National Geodetic Survey). If the former, we apologize for suspecting the confusion, since you are well aware that the USGS set many thousands of disks that are not in the NGS database, and a relatively small number that are. Good hunting!

Interesting find. It seems doubtful to us that this is a property corner. It is a bench mark in the strictest sense, which is to say that it gives the established elevation of the point at which it is set. Cheers,

We found two of them once, in nearly one place, one a full-fledged member of the database, and one not listed anywhere that we've turned up. Both at OA1090. One on each side of the Siuslaw River Bridge in Florence, OR. Cheers,

Duplicate, sorry.