Black Diamond started as a coal mining town in the 1800s. Now, it is considered a ghost town inhabited by two spirits sharing the same nickname, Mary and Sarah.
There's conflicting stories about Mary though I believe the second one. The first states she was hired by a family to be their nanny, but she didn't disclose to her employers that she practice witchcraft. When they found out, they immediately fired her. The next day she was found dead in the mines. How she died is still unknown.
The other has her not only a nanny but one that looked after all the children in the town of Nortonville. Then, all the children died suddenly of mysterious illnesses. The town quickly accused her of witchcraft and was hanged.
Many witnesses over the years have reported seeing a floating bright white apparition near the entrance of the mines. It is believed that she protects children from the dangers inside it. The reports on physical features differ but the similarities have always been that she is either dazzling or bright white. This is how she got the name "White Witch".
Another "White Witch" is said to occupy the Rose Hill Cemetery located on top of a small hill just west of the main entrance to the Black Diamond Park preserve. Sarah Norton, a midwife who died tragically when the carriage she was riding in turned over and crushed her while on her way to deliver a baby, is said to haunt this location. She wasn't know to be a spiritual person and even rejected ceremony.
Her children tried to obey her wishes for no funeral but the towns people decided otherwise. Since she was greatly admired, the entire town of Somersville tried twice to give her a public funeral, but failed when unnaturally fierce storms struck. A third attempt was made, and on this day another fierce storm hit town, but the determined townsfolk decided this time to suffer through the storm and hold the ceremony as planned. And so it was that Sarah Norton was publicly laid to rest within the gates of Rose Hill Cemetery - against her wishes.
Since that day, have reported seeing a white apparition floating between the headstones scattered throughout the cemetery. Sarah Norton hopelessly wanders the cemetery looking for a way to leave. Thus, she shares the nickname "White Witch" with Mary.
The Contra Costa Historical Society does have on record an obituary for one Sarah Norton. The date of death is listed as October 11, 1879 with no cause of death provided.
Sources: East Bay Paranormal and Real Haunted.com