Geology and Tectonics of Santa Catalina Island and the California Continental Borderland

Mark R. Legg, Paul M. Davis, & Eldon M. Gath

Published 2004, SCEC Contribution #875

Objectives: We will visit Santa Catalina Island to examine the outstanding examples of basement rock outcrops exposed on the island, evidence of ancient and active faulting, and explore the most recent tectonic models and earthquake potential for the island and surrounding California Continental Borderland. A visit to the East End Quarry will provide excellent exposure of the "Breccia" used to construct the Long Beach breakwater as well as the volcanic intrusions. We will see spectacular examples of landsliding on the island and will discuss the history of mining and development on this offshore piece of Los Angeles County. There will be three major geological themes for discussion and examination during the field trip: 1) basement rocks and the subduction history; 2) Neogene volcanic rocks and magmatism in the Inner Borderland Rift; 3) Neotectonics and what are the major geological processes occurring on the island today. The rocks to be seen on the island and their structural relationships provide important insights into the geologic history of the southern California continental margin that cannot be easily observed elsewhere. In particular, this field trip will discuss exciting new discoveries of major crater structures in the Inner Borderland and their relevance and potential as "Rosetta Stones" to enable greater understanding of the late Cenozoic tectonic evolution of the Borderland and the Pacific - North America transform boundary. We will have presentations about the island's natural history by experts from the Catalina Conservancy, and evening presentation about the submerged part of the island as viewed from the DSV Alvin.

Itinerary: The trip will start at San Pedro where the Catalina Express will ferry the group to Avalon. At Avalon, we meet the bus and travel to the East End Quarry. From there, we travel to the interior stopping for lunch at the airport where excellent view of the mainland is provided. Then, we proceed north stopping at important Catalina Schist outrcops including Little Harbor before arriving at Two Harbors and the USC Wrigley Institute for lodging and dinner. On Sunday, after breakfast, we hike around the Two Harbors area to see more outcrops and landslides, boarding the Catalina Express for return to San Pedro in the afternoon. Those who may wish to travel to Avalon on the preceding Friday must make their own arrangements for Friday night lodging and meet the group at the bus station by 8:00 AM. PLEASE NOTE THAT CATALINA EXPRESS FERRIES FROM TWO HARBORS ONLY GO TO THE SAN PEDRO TERMINAL. It is also recommended that participants carpool to reduce parking costs at the Catalina Express terminal.

Legg, M. R., Davis, P. M., & Gath, E. M. (2004). Geology and Tectonics of Santa Catalina Island and the California Continental Borderland. In Legg, M. R., Davis, P. M., & Gath, E. M. (Eds.), South Coast Geological Society Annual Field Trip Guidebook, (1, pp. 409) Santa Ana, CA, : South Coast Geological Society