Contra Costa County is a county located in the U.S. state of California, in the East Bay of the San Francisco Bay Area. â–» Focused and ambitious actions are taken to reduce greenhouse gas emissions, improve community resilience, and adapt equitably to a changing climate.This is the ranch home of John Muir, 1838-1914, explorer, naturalist, author and foremost advocate of forest protection and of national parks. This three-story administration building and outdoor plaza is more than a construction achievement; it's a community revitalization effort. Contra Costa County administrators did not say when demolition of the 12story building, one of the tallest in the county, might begin.