A giant monster seemingly made of brown stone, the "rock creature" is encountered on an uncharted planet by Captain Kirk, Mr. Spock, Nurse Chapel, and conman Harcourt Fenton Mudd in 2269 (stardate 4978.5). The creature is over 100-feet tall, has three yellow eyes, two forearms with three articulated claws, and a segmented body that ends in a sluglike tail. It growls with deafening noise. Although alive, it does not show up on Enterprise sensors as a living creature. A second rock creature, which resembles a giant brown alligator with pincer-like claws, is also encountered on the planet.