Silicon valley is located in the northern part of the San Francisco bay area of California. It is called Silicon valley because a man named Don Hoefler wrote for ELECTRONIC NEWS, a weekly tabloid, to describe the technologies being invented there. Silicon Valley has been named that term for about 41 years in 2012. Silicon Valley is important because it was the birthplace of the internet and the first microprocessor.
http://www.netvalley.com/silicon_valley_history.html
http://en.wikipedia.org/wiki/Silicon_Valley