According to Navajo folklore, monsters came into being in the Third World. It happened during a time when men and women lived apart and women used animal horns, long stones, and bird feathers for sex. These women became pregnant when people moved into the Fourth World.
When a baby was born with no head, the people decided to leave it to die. Instead, it grew into the Horned Monster. Another woman gave birth to the Monster Eagle and another birthed the Monster Who Kicks People Down the Cliff.
Another monster was born because a woman who used a skinned cactus for sex gave birth to twins. They had no heads but two holes on top that resembled eyes. They were abandoned but grew to become the Monsters That Kill with Their Eyes.
The monsters hid along paths and roads, killing and eating unsuspecting travelers.
According to Navajo folklore, the monsters had eventually killed most people and First Man sought out the Holy People for help. White Shell Woman produced two twins who could perform miracles and destroy monsters.
Together, the twins set out to rid the land of the animal, rock, and human monsters. The twins became known as Slayer of Alien Gods and Born from Water. The only God that took human form was said to be the size of a mountain. All monsters killed without mercy and nearly killed the entire population.
It is believed the bodies of the monsters slain by the twins turned to stone and make up the large formations now known as Monument Valley in Arizona. A mask depicting the monster slayer of Navajo folklore is still used in ceremonies today as a way to honor this Navajo legend.