Completed in 1915 as Mandan's U.S. post office, the First Street Federal Building followed plans by James Knox Taylor, FAIA. Taylor served as the U.S. Treasury Department's supervising architect from 1897 through 1912. His successor, Oscar Wenderoth, supervised the building's construction and commissioning. A similar but slightly smaller federal building was designed and constructed concurrently at Wahpeton.
Taylor became known as the “national architect” because of improvements in federal design and construction during his 15-year tenure. By the end of his federal career, the Treasury commissioned an average of ten buildings per month nationwide. Taylor participated in the construction of more than 800 federal buildings, helping create a recognizable federal architectural identity.
Taylor sought to harmonize federal architecture with local history, climate, and environment, specifying North Dakota brick for the building. Although smaller and less ornate than many period federal buildings, its main elevation was carefully proportioned to create a dignified, solid character. Iron lamps, recessed windows, and elegant arches contributed to an effect based on unity, scale, symmetry, rhythm, and classical ornament.
The National Geodetic Survey selected the "massive structure" to hold an elevation benchmark in 1931. The marker was installed near the building's southwestern corner, on the southern wall approximately five feet above ground. A 1982 survey team could not locate it, reportedly because a bush concealed both the marker and cornerstone. Another possible explanation is that the team searched the current post office two blocks away. The database was updated in 2007 to report the marker in good condition.
The marker has three rings of text, from outside to inside:
US COAST & GEODETIC SURVEY BENCHMARK
ELEV 1651.368 FEET ABOVE MEAN SEA LEVEL
$250 FINE OR IMPRISIONMENT FOR DISTURBING THIS MARKER.
The building served as Mandan's post office through 1962. Ownership then passed to the Mandan Library District. The library had occupied the World War Memorial Building's basement since 1939; that building now serves as City Hall. After remodeling, the former post office housed the library from 1964 through 2003. The National Register of Historic Places listed it as a contributing structure to the Mandan Commercial Historic District in 1985. A 2004 move took the collection to the Northern Pacific Freight House on West Main Street.
The city solicited purchase proposals in 2003, but interest was limited because remediation of the downtown petroleum plume had not begun. The vacant building was left unheated, prompting preservation advocates to accuse the city of allowing demolition by neglect. It was razed in January 2008 for additional senior housing.