After becoming free, Mason and her daughters moved in with Robert Owens, the father of Charles Owens and a well-known Los Angeles businessman. Her daughter Ellen would eventually marry Charles Owens. Mason worked in Los Angeles as a nurse and midwife, delivering hundreds of babies during her career. Using her knowledge of herbal remedies, she risked her life to care for those affected by the smallpox epidemic in Los Angeles. One of her employers was the noted physician John Strother Griffin. Saving carefully, she was one of the first African American women to own land in Los Angeles. As a businesswoman, she amassed a relatively large fortune of nearly $300,000, which she shared generously with charities. Mason also fed and sheltered the poor, and visited prisoners. She was instrumental in founding a traveler's aid center, and a school and day care center for black children, open to any child who had nowhere else to go. Because of her kind and giving spirit, many called her "Auntie Mason" or "Grandma Mason."