A red pebble in this sandstone tells geologists that Bay Area rivers were flowing backwards (from west to east) when the rock was formed. How can that be?

Learn the history of your homeland while walking along the TRAIL THROUGH TIME, a series of geology videos featuring naturalist Ken Lavin. Sponsored by the Mount Diablo Interpretive Association in partnership with Save Mount Diablo. Videography by Macha Rose. Animations by Tanya Atwater, UC Santa Barbara. Music by Phil Heywood. Produced by Joan Hamilton.