University of Nevada, Las Vegas, doctoral student Matthew Graham discovered it during a nighttime search of Death Valley National park using an ultraviolet light that made the animal glow in the dark, the Los Angeles Times reported Friday.
Scorpions have chemicals in their exoskeletons that fluoresce under UV light, scientists said.
The new species, Wernerius inyoensis, is just over half an inch long, and has proven to be elusive; Michael Webber, another UNLV doctoral candidate who helped identify the species' unique features, said Graham hadn't yet found another.
"People call scorpions living fossils," Webber said.
Scorpions are arachnids, like spiders, and since they evolved around 400 million years ago and their bodies have changed very little since.
They are found all over the world, but in the American Southwest are usually found in dry, sandy habitats.
The specimen discovered at Death Valley will go on long-term loan to the San Diego Natural History Museum, the Times reported.