Blackhawk Ranch was established in 1917 by Ansel Mills Easton and his son-in-law William Q. Ward, in an area east of the San Ramon and Sycamore Valleys. The name came from a famous Irish racehorse named Blackhawk that Easton's family had once owned. The land passed through the hands of several owners, including Raymond Force (the owner of the Caterpillar Tractor Company), the Hawaii-based sugar and pineapple company Castle & Cooke and Howard Peterson (owner of Peterson Tractor).

In 1975, Peterson sold the land to Florida developer Ken Behring, who planned a housing development of 4800 dwelling units over 4200 acres (17 km²) of land. Critics charged that the plan would have various negative impacts, related to urban sprawl, environmental damage and violations of the County General Plan. A group of environmentalists and local residents called Amigos de Diablo organized against the Blackhawk Development Corporation, but were sued for libel. The Blackhawk Development Corporation finally reduced the number of homes planned to 2400 and offered more than 2000 acres (8 km²) of open space to Mount Diablo State Park.