Pretty modern headstone for an 1891 death, you say? That's because Biddy's grave was unmarked for 97 years.
The ceremony on March 27, 1988 was attended by Mayor Tom Bradley, the first African American mayor of Los Angeles, and three thousand members of the First African Methodist Episcopal church.
Here's the news story - http://articles.latimes.com/1988-03-28/news/mn-178_1_black-church
A year later, November 16, 1989, was declared "Biddy Mason Day" in Los Angeles.