As someone who knows this from firsthand experience, there’s a lot of smart, innovative work going on in California’s famous Silicon Valley. It’s the high-tech center of the country, if not the world (sorry Seattle), and it drives a lot of trends and helps to hammer through a lot of old-fashioned thinking. It’s the place where anything seems possible.

Unfortunately, it’s also the place where the notion of high-level female leadership just took a big step backward. As I pointed out here earlier this week when commenting on the abrupt departure of CEO Diane Greene of software maker VMware , it’s never a good day when a female CEO gets pushed out of her job given that there are so few of them around.

Well, the San Jose Mercury News today notes that with the departure of Green,  “the number of women chief executives at Silicon Valley’s biggest technology companies dropped to zero. … Greene’s ouster may have stemmed from a dispute over business strategy, rather than her gender, but the news sent a rumble through the ranks of female managers and others concerned about diversity in the corner office.”

And, there’s no sense that this picture is going to change anytime soon. The Mercury News reports: “ ‘The pipeline is light. It’s not a pretty picture,’ said Wendy Beecham, who runs the Forum for Women Entrepreneurs and Executives, a Palo Alto organization formed to support women in business in the Bay Area.

“ ‘The valley’s abuzz’ about Greene’s departure, said Nicole Woolsey Biggart, dean of the graduate school of management at the University of California, Davis, which conducts an annual survey of women executives and directors at [California’s] biggest public companies. … The UC Davis survey and other studies have repeatedly highlighted the relatively small numbers of women in senior jobs at large firms. Last year, Santa Clara County ranked lowest in the state for the number of women in the top ranks of big firms. … [And] earlier this year, a Mercury News survey found only two women CEOs at the valley’s 150 biggest corporations: VMware’s Greene and eBay’s Meg Whitman, who stepped down from her post in March.”

The question for me is pretty simple: Why is it that Silicon Valley companies can be so over-the-top innovative in technical creativity and business practices, yet so backward and regressive when it comes to gender diversity in the executive suite?