NorCal coast north of SF to Ore. If Ore can build golf on their coast why not Cali?
The CCC, that's why. It is sad though because there is so much potential for something special. The climate is still right too for linksy fescue conditions. Despite the presence of Cypress in Monterey, I would say the California coast is maybe only 10% of what it could be. The dunes north of Reyes and just incredible.
Speaking of "what it could be," I would nominate Northern Michigan for untapped locations for great courses. Yes, there are hundreds up there, but despite sandy golf-scale hills and nice forestry, only a few are great, and only one is greatly conditioned (Kingsley Club). I don't mean to slight some fine conditions and native presentations at other places, but Kingsley is in a world of its own and a model for what really could be.
One more nomination for actually untapped land is the eastern edge of the California Central Valley that I often drive through on CA-4. I once thought the wide open cattle grazed hills looked like the Sand Hills of the west; that was until I was actually in the Sand Hills. The right plot out there could make for some golf unlike that in the rest of CA though. it could be rather rocky and limiting to what can be produced; I'm pretty sure it is not pure sand at least. This is why I said "the right plot." It certainly would be fun to try though, and I would love having a golf course around there that I actually want to play.