Lori, its' a pretty common question on Garden Web and you should be able to find lots of threads about this subject.

I would suggest you learn as much as you can about the habits and life of squirrels (and other pests you anticipate at the mountain resort) while you are trying to come up with plants they won't eat. Like deer, squirrels are difficult to keep out of landscaped areas and there are few plants they won't eat if hungry enough. You may have to try a combination of plants they tend not to eat along with exclusion or repellant techniques.

While this handbook does not have a list of squirrel-resistant plants, it does give lots of information about squirrel natural history and squirrel damage.
http://wildlifedamage.unl.edu/handbook/handbook/allPDF/ro_b171.pdf

As for deer damage, that's easy - not only are there numerous threads on GardenWeb about controlling deer damage, but many states' extension service websites have excellent information about deer control. Try this one from Colorado State University Extension: http://www.ext.colostate.edu/pubs/natres/06520.html

Here is a page that has files on management of a couple dozen other types of pests. Although they don't have tree squirrels, they do have info on ground squirrels and other common california pests. From Univ Calif Extension Agricultural and Natural Resources: http://www.ipm.ucdavis.edu/PMG/selectnewpest.home.html

Have you done a search on Garden Web? How about searching for "squirrel +proof"? lots of people get very aggravated at squirrels. You'll have to read through alot of posts to get what you want, but it's possible. good luck. As I wrote in your other post (in the Landscape Design Forum) ... you can always try plastic plants.