Santa Rosa Geology
Santa Rosa is the second largest of the Channel Islands, and has two
peaks in the 1,500 feet range. It is primarily rolling hills and grasslands, lending itself to successful ranching operations for generations. The Island is primarily sedimentary sandstone, sometimes wind blown into unusual formations, and yielding plentiful fossil records from the Pleistocene era. There is a limited amount of volcanic igneous rock formation on the island.
The most remarkable feature geologically on Santa Rosa occurred in very recent time geologically speaking. In 1812, a year fraught with frightening weather and earthquake disasters, a 1,000 foot rift 100 feet long and 50 feet wide opened up on the island during an earthquake that shook from the Channel well onto the mainland, causing a tidal wave to hit Santa Barbara, and causing severe damage to the Mission in the Santa Barbara foothills. Another older fault lies on the island running from the east to west shores, with the rocks on the north of the fault being younger than the rocks on the south side of the fault, meaning that the south side has more recently been brought to the surface during tremendous seismic activity.
Santa Rosa is also home to a caliche forest, as is its closest
neighbor, San Miguel. A caliche forest is an other worldly appearing mineral formation that has adhered to the lifeless remains of low lying vegetation. The caliche formation are made of rhizoconcretions that form eerie, abstract landscapes of bizarre form. The materials that work together to form a caliche forest are calcium carbonate, sand, gravel, silt and clay.