55 miles northeast of Las Vegas on Interstate 15, a sign indicates  Exit 75, the turn off for the Valley of Fire, Nevada’s oldest & largest state park.  We love coming to this preternatural marvel of nature, named for the amazing red sandstone formations left after immense, shifting sand dunes were formed during the age of the dinosaurs, 150 million years ago.  The oldest rock in the park, though has been dated at about 600 million years old.  Imagine!  Once an ancient sea…