During the last Ice Age the northern Channel Islands were part of one vast island geologists call Santarosae. Sea level was then much lower, and large areas of today’s sea bed were dry. The northern islands were then linked together, though probably not connected to the mainland. Later, when the great continental ice sheets melted, the islands were separated.
During the Pleistocene era, a dwarf species of mammoth roamed Santarosae, and pine and Cypress forests stood on several islands. Today, the fossilized remains of dwarf mammoths on San Miguel and Santa Rosa, and the forests of brittle sand castings known as caliche (pronounced kah-lee-chee), that are found on San Miguel remind us that the Islands were very different long ago. Some plants and animals have developed special adaptations over time to cope with the isolated environment—others remain unchanged. The giant coreopsis is found on all five park islands and on the coastal mainland. Its more common name, "tree sunflower", suggests its size and trunk-like stem. Its bright yellow blossoms are sometimes visible from the mainland during the winter and spring.
The introduction of non-native plants and animals to an island ecosystem can devastate native species. One such exotic is a tenacious South African species of iceplant which found its way to Santa Barbara Island before 1900. Highly salt tolerant, it thrives in arid soil by capturing moisture from sea breezes. It subsequently leaches salt into the soil, producing concentrations of salt that few native plants can tolerate. Today, the iceplant spreads its thick mats over much of the island. Introduced livestock, food animals, and pets have similar impacts on island environments. Escalating feral sheep, hog, cat, and rabbit populations led to damage to—and sometimes elimination of—native plants and animals. The National Park Service seeks to restore those native populations where possible.
The closest island to the mainland, Anacapa lies 18 kilometers (11 miles) southwest of Oxnard, and 22 kilometers (14 miles) from Ventura. Almost 8 kilometers (5 miles) long its total land area is but 290 hectares (about one square mile). Anacapa is composed of three small inlets inaccessible from each other except by boat. For much of the year, Anacapa looks brown and lifeless. With winter rains, its plants emerge from summer’s dormancy and turn green. Sea mammals are often seen around Anacapa's shores. January through March is whale watch season and migrating whales can be seen in the waters near Anacapa. Western gulls, cormorants, black oyster-catchers, and endangered brown pelicans may be seen year round. West Anacapa's slopes are the primary West Coast nesting site for the brown pelican. To protect the pelican rookery, West Anacapa is a Research Natural Area closed to the public. Except at Frenchy’s Cove, no landings are permitted on West Anacapa without written permission from the park superintendent.
Santa Cruz Island
Largest and most diverse of the islands within the park boundary, Santa Cruz Island is about 39 kilometers (24 miles) long. Its land area is about 249 square kilometers (96 square miles). The central valley's north slope is a rugged ridge; the south slope is an older and more weathered ridge. At 730 meters (2,400 feet), the highest of all Channel Islands mountains is found here. Santa Cruz Island's 124-kilometer (77-mile) varied coastline has steep cliffs, gigantic sea caves, and coves and sandy beaches. The shoreline cliffs, beaches offshore rocks, and tide-pools provide important breeding habitat for colonies of nesting sea birds and diverse plants and animals. The varied topography and ample freshwater support a remarkable array of flora and fauna—more than 600 plant species, 140 land bird species, and a small distinctive group of other land animals. Of the 85 plant species endemic to the Channel Islands, nine occur only on Santa Cruz. The Santa Cruz Island ironwood, the island oak, the island fox, scrub jay, and other distinctive plant and animal species have adapted to the island's unique environment. To biologists, Santa Cruz is specially significant for its diversity of habitat, greater than any other of the Channel Islands.
Chumash Indians inhabited Santa Cruz Island for more than 6,000 years. When Juan Rodriguez Cabrillo arrived in 1542, as many as 2,000 Chumash Indians probably lived there. Ranching began on the island in 1839, with a Mexican land grant to Andres Castillero. Since that time the entire island has been privately owned. In 1988 the Nature Conservancy acquired the western nine-tenths of the island, managed as the Santa Cruz Island Preserve. A permit is required from the Nature Conservancy to visit and land on the preserve.
The National Park Service administers the east end of the island as the newest addition to Channel Islands National Park. Favorite visitor activities include hiking, camping, kayaking, searching for the elusive Santa Cruz Island scrub jay, swimming, exploring the island and just getting away from the hustle and bustle of the mainland. The NPS Santa Cruz Island page has addition information.
Santa Rosa Island
The second largest park island is Santa Rosa. Nearly 24 kilometers (15 miles) long and 16 kilometers (10 miles) wide, its 22,250 hectares (53.000 acres) exhibit remarkable contrasts. Cliffs on the northeastern shore rival those of Santa Cruz Island. High mountains with deeply cut canyons give way to gentle rolling hills and flat marine terraces. Vast grasslands blanket about 85 percent of the island, yet columnar volcanic formations, extensive fossil beds, and highly colored hill slopes are visible. Rocky terraces on the west end provide superb habitat for intertidal organisms, including astounding concentrations of black abalone. Harbor seals haul out and breed on the island's sandy beaches. On the eastern tip of the island, a unique coastal marsh is among the most extensive freshwater habitats found on any of the Channel Islands. The entire island is surrounded by expanses of kelp beds. Consequently, its surrounding waters serve as an invaluable nursery for the sea life that feeds larger marine mammals and the sea birds that breed along the coastal shores and offshore rocks of all the Channel Islands. Beneath Santa Rosa's non-native grasslands are the remains of a rich cultural heritage. More than 180 largely undisturbed archeological sites have been mapped. These include several associated with early man's presence in North America. Chumash Indian villages and historic-era camps of early explorers and fur hunters are evident. Some historians think Santa Rosa may be Cabrillo's final resting place.
In the 1840s and 1850s, Santa Rosa was a cattle rancheria. After the cattle industry of old Spanish California collapsed in the 1860s, sheep were brought to Santa Rosa and soon became its economic mainstay. Sheep grazing continued into the early 20th century, but when the island was sold to Vail & Vickers Company in 1902, the sheep were removed and cattle reintroduced. Though the impacts of introduced grains, insects, sheep, pigs, deer, elk, and cattle were severe, examples of Sand Rosa's native plant communities survive. These tend to be restricted to rocky canyons and upper slopes. Native and endemic plants include the tree poppy, island manzanita, and an endemic sage. Native Island Oaks grow on protected slopes, and two groves of Torrey pine are visible near Bechers Bay. More than 195 bird species are found on Santa Rosa. With its extensive grasslands, the island supports large populations of European starlings, homed-larks, meadow larks, house finches, and song sparrows. Shore birds and waterfowl favor the brackish habitat found on Santa Rosa's eastern tip. This marsh and the island's running streams and springs provide habitat for tree frogs and Pacific slender salamanders.
Other terrestrial animals include the gopher snake, deer mouse, and two species of lizard. The island fox may be frequently seen. The endemic spotted skunk— found only on Santa Rosa and Santa Cruz islands— is only rarely observed.
San Miguel Island
Wind and weather sweep across the North Pacific to batter the shores of the westernmost of the northern islands. This creates a harsh and profoundly beautiful environment. San Miguel is about 13 kilometers (8 miles) long and 6 kilometers (4 miles) wide. It is primarily a plateau 120-150 meters (400-500 feet) in elevation, but two rounded hills emerge from its beautiful, and windswept landscape.
San Miguel boasts outstanding natural and cultural features. Some of the Channel Islands' best examples of caliche are found here. Enormous numbers and a variety of seals and sea lions "haul out" and breed on its isolated shores. The Channel Islands' largest land mammal, the island fox, can be seen on San Miguel. San Miguel's fragile treasures include more than 500 relatively undisturbed archeological sites, some dating back thousands of years. Juan Rodriquez Cabrillo, discoverer of California, is believed to have wintered and died at Cuyler Harbor in 1543. Although his grave has never been found, a monument over-looking Cuyler Harbor was erected in 1937 to commemorate his northern voyage of discovery.
In the 1850s Capt. George Nidever brought sheep, cattle, and horses to San Miguel. An adobe he built may be the earliest structure on any of the Channel Islands. Its remains are barely visible today. In 1930 Herbert and Elizabeth Lester became the Sand's caretakers. The family left the island in 1942 after the suicide of Herbert Lester, who had become known as the "King of San Miguel." From the mid-1940s to the mid-1950s the island was used as a bombing range. Staying on the trail is particularly important on this island because live ordnance is still occasionally uncovered by shifting sands.
For half-day visits to the island, the caliche forest is a popular destination. Once you hike from the beach to the island's top. it is about 5.5-kilometers (3.5-miles) from the ranger station to the caliche forest. Caliche is a mineral sandcasting. As with all park resources, it may not be collected. Take all the pictures you want. The island has been greatly altered by extensive sheep grazing, but you can still see an array of distinctive native plant species. Coreopsis and other flowering plants produce beautiful displays in spring.
If you can spend more time on the island, try to make the 24-kilometer (15-mile) round-trip hike across the island to Point Bennett. With binoculars you may see thousands of breeding seals and sea lions (pinnipeds) from an overlook about 1.5 kilometers (1 mile) from the beach. Depending on the time of the year, the California sea lion, Steller sea lion, northern elephant seal, harbor seal northern fur seal, and the Guadalupe fur seal may be seen at Point Bennett. (All except the Guadalupe fur seal and the Steller sea lion breed on the island.)
Seasoned hikers who make this long, cross-island trip to Point Bennett will never forget seeing one of the world's outstanding wildlife displays.
Santa Barbara Island
Santa Barbara Island lies far south of the other four park islands. Small, about 260 hectares (640 acres), and triangular, its steep cliffs rise to a marine terrace topped by two peaks. The highest point, Signal Peak, is 194 meters (635 feet) in elevation.
Santa Barbara Island was named by Sebastian Vizcaino, who arrived here on December 4, 1602— Saint Barbara's Day. Because of the lack of freshwater, Indians did not reside on the island, but they occasionally stopped off there on journeys to other islands. Not until the 20th century was Santa Barbara Island settled to any extent. During the 1920s, farming, grazing, intentional burying by island residents, and the introduction of rabbits severely damaged the native vegetation. During World War II the U.S. Navy used the island as an early warning outpost, and constructed the Quonset hut now used as the ranger station and visitor center. Though non-native grasses including oats barley, and brome dominate the landscape, with protection and encouragement the native vegetation, is recovering. With the rabbits now removed, stands of giant coreopsis are thriving. In places this sunflower grows up to 3 meters (10 reef) tall. In the spring goldfields blanket the island with tiny, bright yellow flowers.
California sea lions and, in winter, elephant seals breed on the island. Birdwatching is superb. Western gulls nest in abundance, and occasionally brown pelicans nest here too. Land birds, including barn owls, American kestrels, horned larks, and meadowlarks, also nest here. Although not commonly seen, the island deer mouse and the island night lizard, a threatened species, live on the island.
Sand Barbara Island offers 9 kilometers (5.5 miles) of trails to explore. A good place to start is the Canyon View Self-guided Nature Trail near the ranger station and campground. A trail booklet enables you to learn about most of the island' s interesting features readily. Then you can explore the other trails on your own. A Park ranger stationed on the island interprets its features and enforces rules and regulations. There is no telephone, but in emergencies the ranger has radio communications with park headquarters.
A park map is available on the park's map webpage.For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.
A geology photo album for this park can be found here.For information on other photo collections featuring National Park geology, please see the Image Sources page.
Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.
Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
9" x 10.75", paperback, 550 pages, full color throughout
The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!
Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.
Information about the park's research program is available on the park's research webpage.
For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.
The NPS maintains a searchable data base of research needs that have been identified by parks.
A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.
NPS Geology and Soils PartnersAssociation of American State Geologists
Geological Society of America
Natural Resource Conservation Service - Soils
U.S. Geological Survey
Parks as Classrooms is the education program of the National Park Service in partnership with the National Park Foundation. It encompasses many different kinds of experiential education programs at national parks throughout the country. Each year park rangers at Channel Islands National Park share the park resources with over 10,000 students in classrooms and nearly again that many at the park visitor’s center.
General information about the park's education and intrepretive programs is available on the park's education webpage.For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.