For me, proximity to Silicon Valley is not a priority. My suggestion is to use land in NW Oregon in the coast range. Most of it is very rugged, but there's some sort-of-flat land in the general vicinity of Saddle Mountain that's currently used to grow lumber. It's close to the beach but far enough not to be in the tsunami zone, and close to highway 26. Water is unlikely to be an issue, and it's close enough to Portland that it's not totally isolated, yet far enough away not be be a suburb.
I think one of the downsides of trying to establish a tech-hub city in the middle of nowhere is that tech hubs tend to have a symbiotic relationship with universities, and the latter are hard to create artificially.