The Farallon Islands, Channel Islands of California and the rocky mainland coast have historically provided hazardous navigational obstacles to shipping. Intermittent fogs and dangerous winds and storms often led ships to rocks, dangerous beaches and islands to be pounded by the Pacific Ocean's Swell and storms. Fierce currents have always swept in and out of the entrance to the Golden Gate as the tide shifts direction. More than 140 shipwrecks have been reported in the waters of the Gulf of the Farallones National Marine Sanctuary.