C&GS T-14 = USGS 76 = Portland 4007
Those early USGS bench marks without the code names, but number only, were generally set in 1896 before they decided to start having the datum code stamped on them with the elevation. Or, in other instances, USGS was very sure that the datum they were using was so close to true sea level that they didn't think they needed to have a datum code for them.
There are some very interesting aspects to this story where the assumed local datums often had some large dicrepancies. One location in Montana was 49 feet too low, a location in Georgia was 33 feet too high, and the Sheridan, WY, datum was 12 feet off.
USGS Deadwood Datum
I have shown this before, but it gives a good representation of a local datum that was established by USGS in the Black Hills of South Dakota and carried into parts of Wyoming as well. The majority of these bench marks were set in 1898. Kurt Luebke and I have recovered these during the past few years.
http://www.penryfamily.com/surveying/usgssddeadwoodbm.html
C&GS T-14 = USGS 76 = Portland 4007
> Those early USGS bench marks without the code names, but number only, were generally set in 1896...
City of Portland datum was established about that time, based on levelling by railroaders coming in from tide gauges at the mouth of the Columbia River. Today there is a little over 3 feet difference between NGVD29 and NAVD88 in the Portland area, with City of Portland Datum falling about halfway between the two.
BTW, that monument is clearly visible in Google Earth Street view.
found this in my news alert.
I don't know if it helps.
I heave some BM research material compiled in 1939 and 1989 for the New Orleans area. Wine I get time, I will browse through and see if there are any BMs of the USGS described.
C&GS T-14 = USGS 76 = Portland 4007
> BTW, that monument is clearly visible in Google Earth Street view.
It is also clearly visible to anyone walking in front of Portland City Hall one fine June afternoon. That is the Mayor's Prius partly visible in the background.
Note that the published City of Portland datum elevation of 78.835' equates to 77.460' NGVD29, and 80.935 NAVD88.