San Miguel Island
Map SatelliteSan Miguel Island is the westernmost of the Channel Islands. Most of the island is composed of marine terraces ranging up to 150 meters (500 feet) above sea level. There are also extensive areas of sand dunes. The wave-cut terraces vary from 3 meters (10 feet) to 10 meters (30 feet) in thickness and were formed during the Pleistocene. Underlying the terraces are various sedimentary and volcanic rocks, related to the Santa Monica Mountains and dating from the Eocene and Miocene to Recent. There are some Miocene andesite volcanics which may have been derived from Castle Rock, probably a volcanic plug, which lies 2.25 kilometers (1.4 miles) offshore.
Some dunes have covered the vegetation which, in time, has led to extensive caliche formations. Both the flora and fauna are relatively depauperate. Some 190 species of native plants have been recorded from the island. Communities include coastal scrub, which covers perhaps half the island, and coastal strand, occupying 10%; the remainder is barren. A total of ten Channel Island endemics occur on the island, though none is confined exclusively to this island. Five are shared with islands in the northern and southern groups: Dudleya greenei, Astragalus miguelensis, Lavatera assurgentiflora, Amsinckia spectabilis var. spectabilis, and Malacothrix indecora (the first three are considered rare). Five are shared only with other northern islands: Castilleja lanata ssp. hololeuca, Galium californicum var. miguelense, Galium buxifolium, Phacelia insularis var. insularis, and Erysimum insulare. (All but the Castilleja are considered rare.)
Zoologically, the island is one of the main pinniped rookeries in the State. Among those species breeding here are the Northern sea elephant, Mirounga angustirostris, California sea lion, Zalophus californianus, Steller sea lion, Eumetopias jubata, harbor seal, Phoca vitulina, and most probably the rare Guadalupe fur seal, Arctocephalus philippi. It is also the type locality for the southern race of the sea otter, Enhydra lutris, and though this is well beyond the otter's present normal range, occasional individuals are sighted in the area.
Among the more noteworthy terrestrial mammals is the island fox, Urocyon littoralis. Additionally, seven species of sea birds nest on the island. As the island is directly affected by the cold California Current, much of the marine biota and some of the terrestrial show affinities with the more northerly coastal species.
The island is exceptionally rich in archaeological remains.
Integrity: Once used for ranching, the island has been abandoned since 1943. Continuing over-grazing apparently led to the extensive dune formations.
Use: Restricted. Educational, research.
Ref: Philbrick, R. N. (ed.) 1965, Symposium on the Biology of the California Islands. Santa Barbara Botanic Garden, Santa Barbara, 363 pp.
October 1976
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman
