Serving with Walker was Robert Doyle, president of Save Mount Diablo. He had succeeded Hornbeck as Assistant General Manager and Chief of Acquisitions for the East Bay Regional Park District. Doyle and Walker strategized about developing public support to expand the Preserve from its original 970 acres (3.9 km²). In 1987 the square-mile Marshall property was acquired and added to the Preserve. Seth Adams, staff for Save Mount Diablo, aided Walker and Doyle as SMD worked to expand the nearby Mt. Diablo State Park with its Morgan Ranch acquisition.