The last hazards to California-bound vessels were the approach and entrance to San Francisco Bay. The Farallon Islands off the mouth of San Francisco Bay were the graveyard of several ships, and the narrow, often fog-shrouded opening into San Francisco Bay was always a danger. Soon after the ship traffic built up, ship pilots who were knowledgeable of the bay were at work boarding incoming (and outgoing) ships and guiding the ships to a safe anchorage in the bay. By 1851 the tangle of ships in the bay had led to the creation of a harbormaster who dictated where ships could drop anchor. Once inside San Francisco Bay, vessels were reported and identified to the people of San Francisco by the watchman with a telescope in a tower erected in September 1849 on Telegraph Hill, San Francisco. The watchman hoisted up the telegraph mast, one semaphore arm for a schooner, two for a brig, three for a ship and two raised about 45 degrees for a paddle steamer. These signals were soon known by most residents.