The California Current is an ocean current in the North Pacific which runs along the West Coast of the United States, moving to the south until it hits Baja, at which point it starts to drift westward. This current is one among a series of boundary currents which move along the earth's continents. The California Current is an example of an eastern boundary current, because it is bordered by land in the east.
The current originates in the North Pacific, where the water is very cold. It is relatively shallow, carrying a load of cold water which stimulates upwelling as it passes along the coastline. As it gets into warmer southern waters, the cold water starts to sink to the bottom, allowing warm water to rise and generating a warm current which travels across the Pacific Ocean. This current links with a western boundary current which travels up the coast of Asia before looping around to North America again.
The series of interconnected currents which circles the North Pacific is known as the North Pacific Gyre. These currents play an important role in the circulation of the ocean, and in the economies along the coastlines they travel past. In California, for example, the California Current contributes to one of the most productive marine ecosystems in the world, with nutrient rich water and some astounding biological diversity. The southward flow of the current also explains why the waters off the coast of California are cooler than waters at similar latitudes on the America's Eastern Seaboard.
The famous foggy days of California are in part caused by the movements of the California Current, illustrating another way in which it impacts life on land. The currents in the North Pacific Gyre also determine where floating objects in the ocean end up over time, as they move along with this spiraling group of currents sort of like soap bubbles caught in the swirl of water around a drain.
It is important to note that there are other offshore currents in addition to the California Current, and sometimes they change direction. Immediately offshore, smaller currents and eddies push water around in a variety of directions. These currents are extensively studied by oceanographers and others with an interest in ocean currents, such as rescue services which want to be able to narrow down the potential location of a disabled ship, a swimmer in trouble, or the body of someone who has drowned.