Channel Islands looking west (Photo: NPS/©Tim Hauf)
Geologist Kirt Kempter leads a fascinating tour that explores the tectonic origin and geology of the four main islands of Channel Island National Park. They are part of the western Transverse Ranges, an unusual east–west trending mountain range in Southern California, representing a block of continental crust that has been rotated more than 90 degrees clockwise during the development of the San Andreas fault system.
A tectonic oddity, diverse rocks of volcanic and sedimentary origin are exposed on the islands, emplaced mostly in submarine environments at the margin of a dynamic plate boundary. Oscillating sea-level rise and fall, correlating with global Ice Age weather cycles, caused the islands to alternately coalesce and separate, with the formation of one large island, Santarosae, during peak Ice-Age cold intervals.
The oldest mammoth fossils date to just over 80,000 years ago, during the Last Glacial Period. As sea level rose more than 350 feet in the past 18,000 years, however, islands formed and the stranded mammoths began to decrease in size due to a shrinking habitat. Fossils of pygmy mammoths preserved on Santa Cruz, Santa Rosa, and San Miguel islands document this remarkable evolutionary trend.
General Information
