PLSO Oregon Surveyor July/August 2020

26 Vol. 43, No. 4 The Oregon Surveyor  | The Lost Surveyor Photo 2: South side of the soldier monument in Lownsdale Square, with benchmark number 2 visible in the top step below the graffiti from recent protests. References • History of the city of Portland’s datum https://www.portlandoregon.gov/ transportation/article/159849 • Tabulation of Official Benchmarks, Department of Public Works, Bureau of Surveys and Drafting, August 1915 • “History of City of Portland Benchmarks,” by H.B. Schminky, June 1956 reported to be 9.5 feet above zero of the current city datum. The building and wa- ter table no longer exist and the site is now occupied by a parking lot and the off ramps from the Morrison Bridge. Later, the City Datum Plane was set to be “56.743 feet below the Initial Point benchmark established by the City of Portland in the southerly quadrant of the top step of the soldier’s monument lo- cated in Lownsdale Square in the City of Portland.” (Schminky) This second bench- mark was the official reference mark to the city of Portland datum plane per Section 5-2002 of the City Public Works Code (date unknown) and this bench- mark still exists today. [Photos 1 and 2] I found very little information about this mark in the documentation. The bench- mark was likely established in 1914 and is stamped Class A Bench Mark No. 00. The 1914 adjustment to the city datum was never adopted. Interestingly, the city’s Online Benchmark Book (portland maps.com) lists the elevation of this disc as 56.664’ rather than the 56.743’ called out in the early documentation. Two blocks from this location is the Unit- ed States Geological Survey Benchmark “T-14” set vertically in the base of the granite pillar on the west face of City Hall on SW 5th Avenue. [Photos 3, 4, and 5] This third benchmark is the point of or- igin for the 1914 City of Portland Bench Level Survey and it is the holy grail of the origins of the city of Portland datum. It was held as the Initial Point of the City of Portland Bench Level Survey in 1914. The elevation of this mark was established in 1896 and is held as 78.835 on the city datum. However, the elevation stamped on the disc was derived by the Coast and Geodetic Survey in 1932. If you run a lev- el loop with the information on the disc you will not be right! This benchmark is currently known in the Benchmark Book as BM 4007 and is stamped on the disc as being set in 1898.  x Continued from page 25 T