Mining opened the earth here, producing 64 million tons of iron ore, leaving a 200-foot-tall pile of reddish rock and a 300-foot-deep lake, creating a magnet for history lovers and fossil seekers.

Mining could also close it. Hill Annex Mine State Park lies beyond a locked gate. Exploration is by organized tour only, and those tours run only during the summer.

"We have a gate, and we don't let people roam around unattended. That piques curiosity," said Jordan Schraefer, manager of this 634-acre park.

A provision in the statute that established the park in 1988 states the mineral rights may be reclaimed if the site once again becomes profitable. "Every year we say this is going to be the last year," Kacie Carlson, the Minnesota Department of Natural Resources' northeast regional naturalist, said during a May field trip.

The site turned a profit from 1913-1978, briefly as an underground mine and then as an open-pit operation. Hematite-rich ore became steel. The sandy overburden built highways. The gravelly middle layer with no immediate use piled up.

John Westgaard has found more than 80 shark teeth in those discarded piles. A volunteer researcher with the Science Museum of Minnesota, he interacts with visitors while he's on-site this summer seeking more fossils from the Cretaceous Period.

"We get a lot of wonderment, especially when I can pull out a box of shark's teeth and tell them I found them right there in Grand Rapids," Westgaard said.

Since last June, Science Museum workers have found more than 300 fossils from the period when a shallow sea covered this part of Minnesota. During that period, when dinosaurs still roamed the Earth, the Mesabi Iron Range was thought to be on the edge of the epicontinental seaway that cut the continent in half.

Most common finds are snails, teeth and clams.

Three never-before-documented finds last season ­— a type of snail, a rough reptile tooth and what appears to be the left upper arm of a reptile — prompted this year's more in-depth field work. It's a job accomplished mostly with hand trowels, rock hammers, dental picks and tweezers.

"We might be able to add new species to our list of animals that lived in Minnesota," Westgaard said. That bit of an upper arm could belong to a sea turtle. "That would be a first occurrence," Westgaard said.

During a May field trip, adults scaled the muddy slope, snapping up bits of anything that looked interesting, filling bags and pockets with rocks. Fossils can be removed from this site because it's on county land near the state park.

Most of their finds were no bigger than the size of a golf ball, nothing like the miners' stories of ammonites (critters related to octopus and squid) too big to fit in steam shovel buckets. One partial specimen measured 4½ feet long and nearly 1 foot in diameter.

"It's always an adventure digging in the ground and wondering what's going to come out next," Westgaard said.

Meanwhile, it doesn't appear as if another land-use switch is imminent.

Kevin Kangas, who is employed by Essar Steel and works for Hill Annex LLC, a project development company, said any plans for the Hill Annex Mine State Park property were still in the project development phase. He said the first step would be for the company to propose a project, which it has not done.

"If we do propose a project, we would want to work symbiotically with the park to stay open," Kangas said.