Roads in the US have been paved with materials that include asphalt/bitumen since at least 1870, when a street in front of the Newark, NJ City Hall was paved. In many cases, these early pavings were made from naturally occurring "bituminous rock", such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphalt-based paving was used to pave Pennsylvania Avenue in Washington, DC, in time for the celebration of the national centennial. Asphalt/bitumen was also used for flooring, paving and waterproofing of baths and swimming pools during the early 20th century, following similar trends in Europe.

Answer this question, if possible (if impossible, reply "unanswerable"): Since what date has asphalt been used for road paving in the US?
1870