Nationwide television audiences will soon find out what many local residents already suspect - western Nevada County is haunted. With several historic buildings that date back to the California's Gold Rush era, such structures are an ideal host for ghosts, according to experts on paranomal activity.So much so, that a pair of TV production companies has selected two separate historic hotels as sets for their documented investigations into the paranormal. Zak Bagans, host of "Ghost Adventures," a weekly paranormal TV series that has run on the Travel Channel since October of 2008, was at The National Hotel in Nevada City …