In the late 1980s and early 1990s, Bob Walker (1952-1992), environmentalist and photographer, a president of the Sierra Club San Francisco Bay Chapter, led the dramatic expansion of the preserve from 970 acres (3.9 km²) to more than 5,000 acres (20 km²). Walker was active as a member of the Board of Directors of the non-profit Save Mount Diablo. In this same period, the Mount Diablo State Park was expanded to the east to join with the Preserve in Riggs Canyon.