San Clemente Island


San Clemente Island at a Glance

County: Los Angeles County 
Distance to the nearest Island: 21 miles to the north is Santa Catalina Island
Distance to the nearest mainland: 41 miles
Height: 1965 feet at Mt. Thirst
Ownership: United States Government
Government Leases:
1901-1905  San Clemente Wool Company
1906-1909  San Clemente Wool Company
1910-1934  San Clemente Wool Company
Size: 56 square miles; 4th in size
Public access: None
Public transportation: None
Native terrestrial mammals:
San Clemente Island deer mouse (Peromyscus maniculatus clementis)
San Clemente Island Fox (Urocyon littoralis clementae)
Non-native terrestrial mammals:
House Mouse (Mus musculus)
Black Rat (Rattus rattus)
Western Harvest Mouse (Reithrodontomys megalotis longicaudus)
Native amphibians: None
Native Reptiles:
Island Night Lizard (Xantusia riversiana)
Side-blotched Lizard (Uta stansburiana)
Endemic Plants:
Brodiae kinkiensis
Tritelia clementina
Eriogonum giganteum formosum
Delphinium kinkiense
Delphinium variegatum thornei
Lithophragma maximum
Astragalus nevinii
Lotus argophyllus adsurgens
Lotus dendroideus traskiae
Malacothamnus clementinus
Camissonia guadalupensis clementina
Castilleja grisea
Galium catalinense acrispum
Munzothamnus blairii

San Clemente Island is the southernmost of the eight California Channel Islands and ranks fourth largest in size. It is 56 square miles in area, 21 miles long, and from two to four miles wide. The island is 41 miles offshore - the second farthest from the mainland. Santa Catalina Island is 21 miles to the north. Mount Thirst, at 1965 feet in elevation, is the island’s highest point. San Clemente Island is in Los Angeles County and is one of three Navy-owned islands among the California Channel Islands. The other two are San Nicolas Island and San Miguel Island (the latter is administered as part of Channel Islands National Park) Two offshore rocks on the north end are named Bird Rock and Castle Rock.

Flora and Fauna:

Seven plant communities cover the island, the larges of which is the grassland community covering about 45% of the island. Maritime cactus scrub is second, covering about 35% of the island’s surface. Island woodland, coastal bluff, coastal strand/dunes, coastal sage scrub and salt marsh communities occur over the remaining 20%.

Fourteen plants are endemic to San Clemente Island: Brodiaea kinkiensis, Triteleia clementina, Eriogonum giganteum formosum, Delphinium kinkiense, Delphinium variegatum thornei, Lithophragma maximum, Astragalus nevinii, Lotus argophyllus adsurgens, Lotus dendroideus traskiae, Malacothamnus clementinus, Camissonia guadalupensis clementina, Castilleja grisea, Galium catalinense acrispum and Munzothamus blairii.

Two native terrestrial mammals, the island fox (Urocyon littoralis clementae) and the deer mouse (Peromyscus maniculatus clementis) occur here. Both are endemic subspecies found only on San Clemente Island.

Physiography and Geology:

San Clemente Island consists of a rugged coastline and precipitous cliffs, especially on the east side and at Seal Cove on the west. A series of about 20 spectacular marine terraces dominates the island’s western portion. Geologically young canyons dissect the island’s coast, and there are only a few sandy beaches, the larges of which is on the southern part of the island. The western shore is dotted with offshore rock islets. Two large offshore rocks on the north end are named Bird Rock and Castle Rock.

San Clemente Island is largely composed of volcanic rocks, chiefly andesite, formed during the Miocene Era. Miocene shales, cherts, and limestone are also present. Interbedded with the volcanics are sedimentary rocks dating through the Pliocene in which fossils of sharks, whales, fishes and seaweeds have been found.