How long can Silicon Valley's economic miracle last?

Is there still gold in the Valley? Click to hear the whole roundtable.

Silicon Valley has gained more than 125,000 jobs in the last five years, its wages are the highest in the country, and it's now the leading exporter of manufactured goods in the United States, but how long can the region sustain such growth?

Several area economists hashed out challenges facing the region's miracle economy at a forum Tuesday night sponsored by the area's Churchill Club.

They pointed out that highways are overflowing, houses are nearly impossible to find, and non-tech workers spend hours on freeways traveling from their Silicon Valley jobs to more affordable outlying areas.

Economist Richard Carlson, vice president of Spectrum Economics, also warned that the Valley is not self-financing, that its reliance on the financial markets and venture capitalists for funding makes it inherently unstable. He said a significant pullback in the markets could sink the Valley's economy.

"I'm not talking about a major pullback, but a case where you can't go back to the well for six to nine months," he said.

Carlson drew laughs when he compared Silicon Valley companies to Velociraptors, feisty dinosaurs known for their quickness and cunning. But he said the wily beasts would have to watch out for the predator waiting to pounce on their weaknesses. He then displayed a Tyrannosaurus Rex with a picture of Microsoft Corp. Chairman Bill Gates.

Carlson explains the technology food chain, including the roles of Silicon Valley Velociraptors, IBM the Brontosaurus, and Tyrannosaurus Bill.

Ted Gibson, the chief economist of California's Department of Finance, warned that poor civic planning and a spate of grass-roots ballot measures could thwart steady growth in the region.

"I worry a little bit more about the forces from within," Gibson said.

Gibson sees some clouds on the horizon.

He also said the area's leaders should plan for the changing work force.

"There are vast numbers of people who don't command the type of wages it takes to live in this area," Gibson said. "That could be a problem."

Economist Doug Henton, president of Collaborative Economics, said most of the Valley's job growth has come not in the software or semiconductor sectors, but in the services area, partly because the region's growing fleet of contract workers and engineers fall under services. Lawyers and accountants also come under that category, he said.

Henton says the workforce structure looks completely different than it did 10 years ago.

"Services are what provide the fuel to the high-tech economy," Henton said.

During the forum, each economist acknowledged what many others have recently: that the economy in the Valley -- where wages have remained high, companies have chugged along, and inflation has stayed in check -- is puzzling and without precedent.

In the end, when asked to rate the Silicon Valley economy a "buy," "hold" or "sell," Henton and Gibson rated it a "hold," and Carlson scored it a "buy."