Rock of Gibraltar may have originated from an escape of North African animals transported to Spain; it is also possible that the original Gibraltar macaques are a remnant of populations that are known to have spread throughout Southern Europe during the Pliocene, up to 5.5 million years ago. Some animals of the Rock have been reintroduced by the Alameda Wildlife Conservation Park who have three Barbary macaques. The Rock of Gibraltar, at the head of the Strait, is a prominent headland, which accumulates migrating birds during the passage periods. The vegetation on the Rock, unique in southern Iberia, provides a temporary home for
Rock of Gibraltar point stands near the south end above the strait at O'Hara's Battery. The Rock's central peak, Signal Hill and the top station of the Gibraltar Cable Car, stands at an elevation of . The near-cliffs along the eastern side of the Rock drop down to a series of wind-blown sand slopes that date to the glaciations when sea levels were lower than today, and a sandy plain extended east from the base of the Rock. The western face, where the City of Gibraltar is located, is comparatively less steep. Calcite, the mineral that makes up limestone, dissolves slowly in rainwater.