The powder magazine, 23' by 67', originally built in 1839 as part of the 1833 - 1875 Detroit Arsenal in Dearbornville, was located about 930 feet east of the eleven buildings shown on the edges of this marker. It was made of local brick, featured 30' walls, vaulted brick ceiling, pegged beams, slate roof, ventilators and two massive, copper-clad wooden doors. The property was purchased in 1883 by Nathaniel Ross who remodeled and occupied it in 1884. His daughter, Mary Elizabeth Ross, who died here in 1950, willed it to Dearborn for museum purposes. Named for her parents, the McFadden-Ross Museum opened on October 27, 1956. A cave-in revealed the well in 1967.