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KU1416 (B USE) and A USE on Queensboro Bridge

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I posted my notes, below, in a recovery entry for KU1416, but figured that I might get more responses here.


For background, marks A USE (not in the NGS Database) and B USE (KU1416) are on the Queensboro Bridge, on columns on opposite sides of First Avenue at 59th Street in Manhattan. There is also a chiseled square, 1670 BOM (KU1415), which I found on the west column. The A and B marks are unusual - two inverted "Y"s whose stems intersect at about a right angle, forming an approximate square that's open at one corner.


Of the two USE marks that were set, I found the one on the west side of 1st Avenue, which looks like it should be the A mark from the original documentation for this mark provided by Papa-BearNYC in his very thorough notes for KU1416. There is absolutely no trace of the B mark on the corresponding column on the east side of the street, which is why I've submitted this post.


Given that the two marks were made at the same time, on the same material, in the same location, and that neither mark was protected from the elements more than the other, I'm surprised that the A mark would still be easily visible, while the B mark would have disappeared without a trace. Both marks would have been high enough off of the ground that they were not likely to have been destroyed by human action, and it would have been unlikely that, over the years, one mark would have been selectively destroyed while one would survive. I've seen marks chiseled in bluestone that have disappeared over a century, but granite should be much more durable.


It's also curious that the NGS datasheet coordinates for the B mark are identical to those of 1670 BOM (KU1415) which is on the west column, with both marks having coordinates listed on their NGS datasheets to the tenth of a second, which is about 10 feet. The east column is much more than 10 feet away from the west column, so if the B mark were on the east column, it should have coordinates that are a little different from those of 1670 BOM. The A and B benchmarks also have the identical elevation to 1/100 of a foot - 1/8 of an inch - in their original description.


Is it possible that there was only one mark established, even though there are two entries in the original description? That would explain why only one mark was included in the NGS database. Or, is it possible that the marks were accidentally "switched at birth," with B actually on the west column, not the east column? Mistakes in a mark's original description, though rare, do happen on occasion.


I hope that my question/concern is clear. If not, I can clarify in a follow-up post. Any information that can help to resolve this puzzle would be very much appreciated. Thanks.

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