Ellen Garrison Jackson Clark was the granddaughter of a freed man who fought in the Revolutionary War. She grew up educated and refined in Concord, Mass. Her mother was friends with families of some of America’s greatest thinkers, including Ralph Waldo Emerson and Henry David Thoreau. So how did she end up in an unmarked grave near Los Angeles for 129 years?Today, L.A. Times features writer Jeanette Marantos brings you the extraordinary story of how amateur historians nationwide got together to find Clark’s final resting place — and finally got her a tombstone.More reading:She was the Rosa Parks of her day. So why was she in an unmarked grave for 129 years?How we got the story of Ellen Garrison Jackson Clark and her courageous, unsung lifeLA Times Today: The ‘Rosa Parks of Concord MA,’ discovered in an unmarked grave in Altadena