One part of California is Silicon Valley.
Alameda County ( [ ˌælə ` mi :d ə ] ) is a county in the state of California in the 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 . The region has expanded to include the southern half of the San Francisco Peninsula in San Mateo County , and southern portions of the East Bay in Alameda County .