Although Silicon Valley's San Mateo County ranks fifth among the nation's largest 334 counties when it comes to average weekly wages, it posted the largest jump in first quarter salary over the previous year, according to the Bureau of Labor Statistics. Home to tech names like Oracle, Electronic Arts and Facebook, the county posted a 14.8 percent increase in average weekly wages during the first quarter. That’s far higher than the national average increase, which was a scant 0.6 percent during the period. The weekly wages include base pay, exercised stock options, bonuses and other forms of compensation. Although the BLS didn’t offer reasons why San Mateo County, in particular, generated such a sizable jump, one contributor could be Facebook's IPO. Consider this: Facebook went public in May of last year, two months after the March 2012 comparison data was gathered. Privately held companies tend to pay less in salary but often offer stock options as a form of compensation. In November, Facebook's IPO lockup expired – and employees and other investors could sell pre-IPO shares on the open market. Then during the fourth quarter, San Mateo County saw a 107 percent increase, according to a San Jose Mercury News report.