 The prison guards facilitated the keepers to blow the fog horns as they were in advantageous position stationed on the elevated watch towers; the guards who were in position to see "a bank of fog started to roll through the Golden Gate", would inform notify the keepers so that the fog horns could be activated.The leading marks which guide the ships while entering the island are the lime point which is east and the black point which is lime north.The island itself is interspersed with several buildings and military towers.