This one is close, and depends on where you are measuring "las vegas" to be. I did measurements from wherever Wikipedia considers the center of the city to be. From this point, Grand Canyon is 61.95 miles away, and Death Valley is 67.07 miles.
I thought for sure Arches was closer to Salt Lake City but after checking distance on google maps like you said Capital Reef is closer. by only 12 miles!! intriguing concept for a quiz