Hey, average salaried worker in San Mateo County, can you spare a dime?

You are, after all, now working in what could officially be dubbed Fat County, after word Wednesday that the county saw a 107 percent spike in average weekly income in the fourth quarter of 2012.

"In my 10 years here, this is the biggest jump I've ever seen," said David Hiles, a supervisory economist with the federal Bureau of Labor Statistics, which tracks employment and wages for each of the nation's more than 3,000 counties based on reports filed by employers. "Keep in mind that this is not just a measure of base pay but of what actually was paid out to employees, so big bonuses and stock options could have contributed."

Which has led economists to theorize that the jump is due to Facebook.

Headquartered in Menlo Park, the social media giant had its IPO in May 2012. But it wasn't until November that employees could cash in stock options, which they did big-time -- exercising 51 million shares to the tune of about $1 billion, which was included in the "wage" total.

Not that everyone working in San Mateo County is bringing home anything close to what those Facebook employees took in.

"I'm a consultant, so I pretty much work for free," joked Danny Cruey, who does marketing and website work for the San Mateo Area Chamber of Commerce. "But it doesn't surprise me to see that jump in average salary because there are startup companies popping up around here every day, and a lot of intellectual property and innovative people running around.

"I already knew there are a lot of wealthy people working in San Mateo County," he said. "But I don't see it in my paycheck."

Ruth Kavanagh with the state Employment Development Department, which also tracks wages in the county, said that while she could not talk specifically about Facebook or any other employer, a large or sudden addition of bonuses or stock options at one company could be a factor behind the dramatic rise in average salary.

"Theoretically, it is possible for a very large employer to have some impact on the overall wages in the county," she said. "But there's a whole variety of things that can cause wages to go up and down, including the ratio of full- and part-time workers, so I can't really speculate on what's behind this particular rise."

San Mateo County's bulging weekly salary translates to an average of about $168,000 a year for workers in the county. And as bloggers have pointed out, that makes San Mateo's average paycheck more than 50 percent higher than the next highest county, New York County, also known as Manhattan. In the fourth quarter of last year, those poor working stiffs in the Big Apple averaged a mere pittance of $2,107 a week, or roughly $110,000 a year.

Cue the violins.

Contact Patrick May at 408-920-5689; follow him at Twitter.com/patmaymerc.