 The largest absolute increase occurred during the decade of the 1980s (over 2.1 million person increase), attracted to job opportunities in part by the expansion taking place in Silicon Valley and the Cold War era expansion of the defense industry.The 2010 U.S. Census revealed that northern California grew at a faster rate than Southern California in the 2000s with a rate slightly higher than the state average.The U.S. National Park System controls a large and diverse group of parks in northern California.