It's actually not quite that bad, but there are some areas where men outnumber women by over 40% [0]. The ratio is a little better in Silicon Valley, at about 1.14:1 [1]. The SF/Oakland/Hayward metro area fares a little better at 0.93:1 overall [2], but that doesn't take into account how difficult is is to access SF from the East Bay and vice versa. It doesn't take much of a skew to really mess up the ratios.
When it comes to dating, simple gender ratios might not paint the complete picture because it's not just any man:any woman. Frequently, the prospective partner has to have a similar socioeconomic background: I'm not in the Valley so I don't know if that ratio is in the ball park of 1.14:1 for the "goes to Silicon Valley" male archetype