Geologists think this island was formed by underwater
volcanic activity. Pressures beneath the earth's surface uplifted this island
which has never had a land bridge to the mainland or the other islands. During
different periods of the uplifting process, wave erosion caused several marine
terraces which are evident today. The island was submerged during the Pliocene
or early Pleistocene eras, and therefore the colonization by plants and animals
began only within the last several hundred thousand years. The island is
made up of tuff and breccia type rocks. The soils of the terraces consist
mostly of silt and clay.
Santa Barbara Island is roughly triangular in
outline and emerges from the ocean as a giant twin-peaked mesa with steep
cliffs. Marine terraces slope away from the two rounded hills, Signal Peak
and North Peak. Offshore, there are two named rocks, Shag Rock off the northerly
shore, and Sutil Island off the southwest end. Santa Barbara Island has no
well developed sandy beaches. A few narrow rocky beaches surround the island
at various points, and most of these are submerged at high tide. Precipitous
cliffs drop to the sea around most of the island. Along the eastern side
of the island are six named canyons: Cliff Canyon, Landing Cove, Cave Canyon,
Middle Canyon, Graveyard Canyon and Cat Canyon.
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