I'm not particularly well informed on the actual logistics of mounting a secession from the rest of the US, although at the very least I would imagine securing water rights would itself be a significant challenge for SV, but I very much doubt the "disruptors" in SV have the wherewithal to stomach such an endeavor.
I'm not super familiar with the geography there but I'd imagine everything west of the rockies (is that the right mountain range) would go with California and I thought that this was the source of the water.
I believe a large part of Northern California's, and by extension Silicon Valley's, water comes from the Sierras. The communities of the Sierras, as well as those of the Central Valley which separates Northern and Southern California, tend to be fairly conservative. They also have high rates of firearms ownership. I don't think they would be too keen to join in on a hypothetical SV secession.
