The road sign reveals that the astronauts are near Reno.
In “I Shot an Arrow into the Air,” the crew believes its damaged spacecraft has crashed on an uncharted asteroid. The surviving astronauts struggle across a barren landscape, ration water, and turn against one another. Officer Corey eventually climbs high enough to see telephone poles and a sign identifying Reno, exposing the twist: they have been on Earth all along.
The sign places the desert 97 miles from Reno, Nevada. That detail is why Reno—not Las Vegas, Denver, or another suggested city—is the canonical quiz answer. The episode’s apparent alien landscape was filmed in Death Valley, whose stark terrain helped sell the illusion of an extraterrestrial world.
The episode is the fifteenth installment of the original Twilight Zone and first aired on January 15, 1960. Rod Serling adapted a story idea by Madelon Champion, reportedly buying the premise after she approached him in public. Its ending, in which a familiar Earth landmark recontextualizes the entire adventure, is often compared with the later twist in Planet of the Apes.