Hoof prints on a Malad Gorge cave ceiling have been rediscovered and documented as tracks from extinct North American horses.

An Idaho State University professor says the prints, which protrude from the ceiling, were made about 1 million years ago as horses stepped through a marsh in part of what now is Malad Gorge State Park in south-central Idaho.Park officials are concerned the blasting required for a proposed hydroelectric project on the Malad River could alter the rock formations along the unstable cliff.

The hoof prints were located after members of a longtime ranching family told park officials they used to view them as they walked to go fishing.

The horses might have been running ahead of the lava flow that soon filled their deep prints with melted rock, said William Akersten, ISU curator and associate professor of vertebrate paleontology, in a three-page written report.

The flow left a massive layer of basalt on top of older layers of rock that form the high canyon walls of the gorge.

Through the ages, the softer sediment between the basalt layers - made of baked bog - eroded away, exposing the underside of the younger flow with the natural molds of the horse tracks.

"As far as I can tell, this mode of trackway formation has never been mentioned in the scientific literature and appears to be absolutely unique," Akersten said in the report.

The most pronounced set of tracks was made by a horse traveling due north. The animal either was running or had slippery footing, Akersten said.

Akersten and another professor from the Idaho Museum of Natural History at ISU looked at the prints in October. This month, they confirmed they were made by extinct horses similar to today's equines.

Park officials were told of the prints this summer during a nature program open to the public.

Sisters Peggy Bennett Smith, 68, of Hawaii, and Gracie Bennett Goodlin, 66, of Texas, told a park ranger they knew the general location of some pony prints molded in rock.

Their grandfather, S.W. Ritchie, started a nearby ranch in 1909 and the girls were raised there, said their brother, Craig Bennett, 57, a retired Buhl physician.

Following the sisters' directions, summer Ranger Dave Middleton hiked into the gorge to a shallow, 3-foot-high cave with hoof prints sticking through the ceiling.

Park Manager Kevin Lynott said the prints are about the same size as the hooves of today's horses.

"It's definitely a link between the (3.5 million years old) Hagerman fossil horse and the modern horse," he said.

Ranger Jack Yarbrough said he has walked past the low cave for seven years.

"We'd have never found these things if they (the Bennett sisters) hadn't come to that program," he said.

"It was just something all our family knew about, kind of like Christmas and New Year's. It was just there," Craig Bennett said. "There were about three or four trails you could go down into the canyon on. We went fishing there a lot."