In what might signal a final push by Silicon Valley, an environmentally-oriented investor group today released a manifesto from 66 “leading investors” opposed to California’s Proposition 23. The group is said to manage more than $400 billion in assets.

In a conference call with reporters, venture capitalist Alan Salzman called clean technology the “next industrial revolution,” and that “California is at the epicenter.” To prove his point, Salzman pointed to $9 billion invested in “clean-tech” since 2006, in California alone, and he called Prop 23 “antithetical” to the transition that global industry is now undergoing, claiming that 20% of total venture capital funding is flowing to clean-tech, of late.

Salzman’s VC group, VantagePoint Venture Partners, is backing California companies such as electric-car maker Tesla Motors and BrightSource Energy, which was recently cleared to break ground on a major solar-thermal generation project in southern California.

The news call was organized by CERES, a Boston-based business group that promotes environmentally enlightened investment. Chris Davis, who directs investor programs for CERES, said that Prop 23 would be tantamount to a repeal of the state’s fundamental climate strategy and “a huge step backwards for California and the United States as a whole.”

“You simply don’t want to project an image of policy uncertainty in a global marketplace,” said Davis, “because capital can move elsewhere too quickly, to places with more stable commitments to clean energy policy.”

“This isn’t about wearing hemp and adopting a new kind of lifestyle, Salzman added. “It’s about using the power of technology to modernize the antiquated way we do things, so that we do them better and cheaper.” Salzman may not be wearing hemp but he’ll be rocking out tonight, when he hosts a private fundraiser, with Elvis Costello performing.

At the same time, as Dan Morain writes in a useful analysis for the Sacrament Bee, money may be drying up for the “Yes” campaign, funded mostly by oil & gas interests, while Morain’s tally has opponents closing in on their $20 million goal.

At a recent gathering of environmental journalists, Gloria Gonzalez, Americas Editor for Environmental Finance magazine, told me that Prop 23 was being watched and discussed around the world, as governments and investors alike look for a signal from California. The negative polling on 23 may already be sending that signal.

Meanwhile, some are saying the more permanent threat is posed by Proposition 26, which would require a two-thirds vote to approve any kind of government fees, including those imposed by AB 32, the state climate law that Prop 23 is designed to suspend. Asked about that, Davis, who also represents the Investor Network on Climate Risk, said other environmental groups, such as the Sierra Club, are mobilizing against that measure. Wouldn’t it be something if, after all this hoopla, Prop 23 turned out to be a really expensive diversionary tactic.

Climate Watch producer Gretchen Weber is watching the money flow and updating our interactive map, showing major donations on both sides in the Prop 23 trenches.

View Top California Proposition 23 Donors: Yes and No in a larger map