Eight Keys to Eden ♦ By Mark Clifton

When Earth loses contact with the colony planet Eden, an expedition is sent to find out why. Even though the planet has been determined to have no hostile properties, the second expedition is astonished to find no evidence of the colony. The colonists are spread out, naked, wandering dazed among the bushes, with no sign of any of the technology they brought from earth. - Summary by Dale Grothmann