Where is the cave that was first documented in the oldest continuously published monthly magazine in the United States?
Gypsum Cave: Gypsum Cave is a cave located east of Las Vegas. Gypsum Cave:  It was first documented by Mark Raymond Harrington in a 1930 edition of "Scientific American". Scientific American: Scientific American (informally abbreviated SciAm) is an American popular science magazine. Scientific American:  It is the oldest continuously published monthly magazine in the United States(though it only became monthly in 1921).
east of Las Vegas