In 1891, Biddy Mason was laid to rest in an unmarked grave in Los Angeles. That wasn’t unusual for a woman born into slavery, but it was remarkable for someone as accomplished as Biddy. After winning her freedom in a court battle in 1856, she combined her nursing skills with wise business decisions to make a small fortune. As she observed the plight of immigrants and prisoners, she reached out to them, investing in charity so frequently that people began lining up at her house for help. In 1872, just sixteen years out of slavery, she and her son-in-law financed…