>just west of woodside there's hundreds of square miles of completely undeveloped land
And there are good reasons it's "completely undeveloped." Those include:
* No public sewer. So you'll need septic tanks. And the county regs that took effect a few years ago made it more difficult to install a new septic tank even for a single-family home, let alone whatever high density project you're envisioning.
* No public water. CalWater's Bear Gulch district (aka municipal water) extends only to the town boundaries on the east side of the hill. Skylonda Mutual on the west side of the hill keeps issuing boil-water notices when their (limited) water supply gets contaminated and out of compliance with state law. La Honda was trucking in water, or came close to it, during the recent drought.
* No DSL or cable Internet. Even inside town limits there are some areas that don't have Comcast (low population density, hilly terrain) or AT&T DSL (too far from switch, but you can get POTS). Hope you enjoy wireless!
* Limited access in the winter due to roads carved out of the hills over 100 years ago, not up to modern construction standards, that are prone to landslides. Skyline around route 9 was still one lane control last I checked because of last year's collapse, which was different from the previous collapse.
* Prone to wildfires in the summer--there was a wildfire off of Bear Gulch Road a year or two ago.
* No public transport.
* Distance from employers. I can't think of any large employers west of I-280, so you'd have to cross the peninsula on gridlocked surface streets or join I-280 gridlock north or south. Probably an hour drive to Google or almost that to Facebook.
* NIMBYites among the locals, who already say it's too congested.
* Subject to excessive zoning restrictions if inside town limits. This is only inside Portola Valley, Woodside, Los Altos, Palo Alto, Los Gatos, etc., and it's true that most of the land is county, but some of those town boundaries stretch to Skyline. If you're inside town limits, you'll need something like 5-acre to 15-acre parcels for a single family home. This is the very definition of low-density housing.
* Prone to landslides. The San Andreas fault runs along the base of the hill, and the Pilarcitos Fault and others spiderweb through the hills. This can be solved with the application of funds, but it raises building costs.
* The big one, if they can find a way to screw with you, is the California Coastal Commission, which views every act as illegal "development." And it has a bigger budget than you. You will not win. State law is not on your side. https://pacificlegal.org/commission-creep-rule-dis-functiona...
But good luck!