California is a state in the Western United States, lying on the American Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and an international border with the Mexican state of Baja California to the south. With nearly 39 million resiā¦California is a state in the Western United States, lying on the American Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and an international border with the Mexican state of Baja California to the south. With nearly 39 million residents across an area of 163,696 square miles, it is the most populous U.S. state, the third-largest by area, and most populated subnational entity in North America.