SAND DOLLAR SECRETS   The Pacific Ocean once lapped against the Sierra Nevada foothills. Here's the story of how the Bay Area eventually became dry land with two bedrocks.  Join us on 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.