About 150 antelope, apparently disoriented by dense fog, plunged to their deaths after wandering single file off a 100-foot cliff in the southwest corner of Wyoming.

"The fall is a natural phenomenon," Wyoming Game and Fish District Supervisor Phil Riddle said Thursday. "It's just another example of what big game animals must deal with on a daily basis."Tracks in the snow indicated that after one antelope fell off the fog-enshrouded cliff, the rest followed one by one, he said.

The bodies are piled about four deep in a 400-square-yard area about three miles northwest of Green River.

Most of the antelope were fawns and does, although there were a few bucks. Most died from broken necks immediately in the drop, he said. About 15 antelope walked a short distance from the pile before dying. Game and Fish officials killed five others that were still alive Sunday afternoon.

Game and Fish officials are asking people not to disturb the area so they can study it. Archaeologists from the University of Wyoming and Western Wyoming College will look at such things as how long it takes for the animals to decay and how much predators eat, Riddle said.

The group was part of the 30,000-animal Sublette herd that roams the area north of Green River and Rock Springs.

A similar event happened three years ago when 70 antelope fell through ice and drowned in the Green River.