Cowell Ranch/John Marsh encompasses 3,659 acres of natural habitat, wildlife, and unique cultural features, including the historic John Marsh Home. John Marsh lived on the property from 1837 to 1856. He was the first American Citizen to settle in what today is Contra Costa County. He was a medical doctor and developed Rancho Los Meganos as a large cattle ranch. The John Marsh Home when completed in 1856 was considered the "finest ranch home in California". Through the efforts of concerned citizens as well as the Trust for Public Land and other entities, Cowell Ranch/John Marsh is one of California's newest state parks, although currently not open to the public.