2100 - 10th Avenue is a Victorian house at East 21st and 10th Avenue, part of the 10th Avenue Historic District. According to the Friends of Bella Vista Park website, it was built in 1891, and designed by John J. & Thomas D. Newsom. 1 (Zillow and other county record-based sites incorrectly say it was built in 1898.)
The house was originally built as a single-family dwelling. Some time between the 1912 and 1928 Sanborn maps, it was divided into a duplex. As with many locations, the address was renumbered several times. At the time of construction, it was 1554 - 10th Ave. The 1912 Sanborn shows the old 1554 and the new 2102 addresses; the 1928 map has 2100 and 2102 for the two units. Presumably it has been combined back into a single-family dwelling, as there is only one address, 2100.
The first directory listing found from the 1892-1893 directory lists Charles R. Johnson, vice president, Fort Bragg Redwood Company, San Francisco. Johnson's obituary calls him one of the founders of Fort Bragg. At the time of his death in 1940, he was living in San Francisco. 2
Some long-time residents were Flora B. Preston and William Newbigging Preston, who lived there from at least 1925 to 1944. William was an electrician for PG&E.