There is a place called Neah Bay in about the most northwestern place you can get in the continental United States. Its also on an Indian reservation. They used to have an airforce base. That base was built to support a hollowed out mountain where they could actually launch jet airplanes. Its really quite scenic and faces the Pacific Ocean (but high up), and its BIG. I suspect that this installation is still there (probably with big steel doors, etc to keep it safe for eternity). So, If you really want to hide out I suspect this would be the place to go. I don't think the Indians are doing anything with it and would probably be willing to give somebody the chance to either buy, or lease, the facility. You could probably stick over 100 people in this one.
There is another installation in a place called Salt Creek. Its currently a county park. It used to have a base, called Camp Hayden, to support it. This one has a number of hollowed out places that were built in WWII to guard the entrance to Puget sound (amongst other things they had 6/8 inch guns installed (now all scrapped out). The hollow places, however, are still there and you can actually drive through a couple of them. The state has also taken over parts of it as, at one time, they thought this would be a good safe place to hideout if war comes and they keep their big steel doors pretty well locked up. I have been told that they have also stored literally tons of paperwork, etc. in there. Still, if you have the bucks I suspect you could work something out.
There are any number of these places still existing. The Oregon coast also has a bunch of them as does puget sound. Port Townsend
has several such places too. Thought I would just make a couple of suggestions if you want to hide out.
Just a thought.............