The Hollywood Reservoir is nestled in a basin surrounded, usually, by dusty brown hillsides, broken up by the occasional dry wisp of shrubbery. Not these days. After yet another burst of rain the other day, the hills were transformed into lush fields of knee-high grass, spotted with purple flowers. And the reservoir? As high as it has been in years. In Northern California, snow could be seen on top of Mount Diablo outside San Francisco last weekend. Across the state, dams are under siege and reservoirs are overflowing.