Tectonic plates are large-scale pieces of the Earth’s outer shell that move over the mantle. Their movements are responsible for much of the geology we see on the planet today. California’s coastal range was formed from a series of tectonic activities. Subduction is the process where two plates converge and one plate moves underneath the other, and this can form volcanoes that produce new rock. Around 85 million years ago, a series of ancient tectonic plates subducted underneath the North American plate, creating much of the rock that forms California. Subduction also resulted in a process called accretion, where marine sediment was scraped and deposited on the western edge of California, which contributed to the coastal range. Around 30 million years ago, one of the last ancient tectonic plates to subduct under the North American plate, the Farallon plate, was split into the Juan de Fuca and Cocos plates by the Pacific plate. The contact between these plates formed a large fault line called the San Andreas fault, a major transform boundary between the Pacific plate and North American plate that cuts through much of the coastal range of modern California. Then, around 8 million years ago, the Pacific plate broke off and carried pieces of Coastal California northwest, including Los Angeles, San Francisco, and Santa Barbara, and created much of what we now recognize as the California coastline. Some of the common rocks found on the California coastline are sandstone, shale, serpentinite, schist and granite.

The Pacific Ocean is a major water resource that California uses for a variety of reasons:

Fishing - Commercial and recreational fisheries are an important part of California’s economy and culture.

• Commercial Fishing: In 2011, California’s commercial fishery industry provided around 120,000 jobs to the state and netted around $201 million dollars for the local economy. California’s South and Central Coastal regions focus mostly on high volume, low-cost pelagic fish like sardines and anchovies. California’s Northern Coastal region is more active in catching lower volume, higher-cost species like Dungeness Crab and king salmon.

• Recreational Fishing: Ocean sports fishing is another major source of economic activity in California, providing around 22,000 jobs and bringing in around $870 thousand dollars (as income) for the local economy. However, a 2010 study from the State Water Resources Control Board’s surface water ambient monitoring program (SWAMP) found that around 37% of sampled locations in the North and Central Coast had high mercury concentrations.

Aquaculture - California has aquaculture facilities on the coast that generate around $102 million dollars. These facilities help produce sustainable seafood. Well-managed shellfish farming can improve the water quality of their plots, as they filter the water when they feed. Mussels, clams, and oysters are commonly grown in San Diego Bay and Santa Barbara. Aquaculture has also been used to restore populations of endangered species like white abalone and Olympia oysters.

Nuclear Power - California has had 2 nuclear power plants by the coast, the Diablo Canyon Nuclear Power plant and the San Onofre plant. These plants were established close to the shore so billions of gallons of oceanwater could be used each day to cool the plants. However, these plants have had deleterious impacts on the coastal ecosystems. Many fish have been sucked into cooling the plants and died. In addition, the water these plants pump back out are much warmer than what is taken in, which causes stress on marine life in the area. The San Onofre plant closed in 2012 due to a radiation leak, and the Diablo Canyon is set to close in 2024 and 2025 due to its effect on the environment.

Groundwater- Coastal habitats are continuously shrinking due to human development and rising sea levels. This loss of coastal habitat may cause an increase in coastal flooding, which would lead to saltwater intrusion into groundwater aquifers. The infiltration of saltwater into groundwater aquifers could alter inland habitats and communities as well as agricultural practices. Coastal ecosystems provide an important flow of groundwater that carries dissolved salts into the ocean.