California’s Silicon Valley is a microcosm of America’s new extremes of wealth and poverty. Business is better than it’s been in a decade. Facebook, Google and Apple have minted hundreds of new tech millionaires. But not far away, the homeless are building tent cities along a creek in the city of San Jose. Homelessness rose 20 percent in the past two years, food stamp participation is at a 10-year high, and the average income for Hispanics, who make up a quarter of the population, fell to a new low of about $19,000 a year — in a place where the average rent is $2000 a month.