Silicon Valley is outside a populous region.
California ( [ kælᵻˈfɔːrnjə , _ - ni.ə ] , ) is the most populous state in the United States and the third most extensive by area . The San Francisco Bay Area ( referred to locally as the Bay Area ) is a populous region surrounding the San Francisco and San Pablo estuaries in Northern California . San Jose, California . With an estimated 2015 population of 1,026,908 , it is the third most populous city in California ( after Los Angeles and San Diego ) and the tenth most populous in United States . Silicon Valley is a nickname for the southern portion of the San Francisco Bay Area , in the northern part of the U.S. state of California .