John Marsh was born June 5, 1799, in Massachusettts and came to California in 1836. He was a doctor. In 1839, he became owner
of Rancho Los Medanos at the foot of Mt. Diablo near present-day Antioch, California. He lived a solitary existence, though
taking some interest in politics and favoring California's incorporation into the United States. He was murdered September
24, 1856, on the road between his rancho and Martinez.