Our bike tires grind through loose sand as birch trees streak by in flashes of white. A few more hills, and we dip down on hard-packed iron-red dirt, curving around large rocks. Suddenly, the view yawns open. Before us, there's a beguiling deep-green lake and not a soul in sight.

The emerald color and astonishing clarity hints that this isn't one of Minnesota's sky-blue lakes. It's an open-pit mine. Or was.

There's a full chain of mine lakes within 5,000 acres that make up Cuyuna Country State Recreational Area. The land was once deemed wasteland, scarred and ravaged by iron ore mining. Yet in the 30-plus years since the mines were abandoned, nature has taken over. Empty pits have filled with crisp spring water. Forests grew back. Excavation piles 200 feet high became wooded scenic hills, offering sweeping overlooks.

Paddlers, divers and anglers have enjoyed these lakes — and hikers have enjoyed trails — ­since the state recreation area opened in 1993. Now it's a mountain biking hub, as well, with more than 22 miles of trails that opened two years ago.

"People are coming from all over and loving it," said Hansi Johnson, a regional director with the International Mountain Biking Association (IMBA) based in Duluth. His organization has ranked Cuyuna Country trails among the world's top five ride centers. The "ride center" designation refers to large-scale projects that offer excellent trails designed specifically for the sport.

"It's the mining landscape that makes it unique," said Cuyuna's park manager, Steve Weber. "It offers outstanding views for mountain bikers and hikers."

Moreover, the state recreation area offers boating, paved-surface biking and even a chance to visit a nearby simulated mine.

From industry to recreation

Cuyuna is among a few places nationwide that have turned former industrial sites into recreational hot spots, where the hardscrabble past adds to their modern-day appeal.

"It's a way to reuse the land in a positive way," Johnson says.

In Santos, Fla., a former quarry and barge construction site also has been recycled into a ride center for mountain bikers. More than 60 miles of hiking, biking and horse trails thread along limestone ledges, through ferns and pines, and across dirt-pile jumps and obstacles in the free ride area of Vortex Quarry.

An hour south of St. Louis, the vast subterranean Billion Gallon Lake beneath Bonne Terre, Mo., attracts people from around the world to see abandoned lead mines. With 500,000 watts of eerie underwater lighting, tourists in boats or on dive tours can see calcite falls, plus ore carts, jackhammers and even a timekeeper's shack crisply preserved in 58-degree water.

It's as though a ghost town met Atlantis. Or as owner Doug Goergens puts it, "part Pompeii, part Lara Croft."

St. Cloud looked to Barre, Vt., another granite-producing region, when it embraced its industrial history and developed Quarry Park and Nature Center on the city's southwestern edge.

Barre claims the world's largest quarry, Rock of Ages, which plunges 475 feet from cliff top to quarry floor. Visitors can go on quarry tours, visit a granite museum, and head to Millstone Hill Touring Center with 70 miles of trails weaving among 1,500 acres and more than 75 small quarries. Campers stake out tent sites among rock piles and gather around fires that crackle and snap in granite-lined pits.

While St. Cloud's Quarry Park is much smaller — 684 acres, 30 granite quarries and no camping — it's still easy to find a private picnic spot overlooking serene, water-filled quarries. Hikers choose trails through marsh and woods, climb up to overlooks or follow the whoops and splashes that echo from the 110-foot-deep swim quarry where daredevils leap from rock ledges.

On hot summer days, cool air wafts from crevices in "grout" piles of discarded stone like primitive air conditioning, a good way to cool off after grinding along mountain biking technical trails. Some of the rocky surfaces are estimated to be a billion years old, pushing up through the earth and harboring surprises like prickly pear cactus that blooms in early summer.

Rock climbers, scuba divers and trout fishermen also can head to quarries designated for each sport at Quarry Park. Interpretive displays explain parts of the granite industry, including a massive derrick that towers above the parking lot, while stray metal cables and unnaturally block-shaped rocks remind visitors these are not ordinary Minnesota woods.

Dive underwater at Cuyuna

Water-filled quarries and mines can provide ideal scuba dive spots with unusual artifacts, challenging depths and stunning clarity thanks to rock-filtered spring water and a lack of vegetation that often clouds natural lakes.

While a typical Minnesota lake has 4 to 6 feet of visibility, "in the [Cuyuna] mines we have between 25 and 50 feet of visibility," says Todd Matthies, owner of the Minnesota School of Diving in Brainerd.

Cuyuna offers at least 50 dive sites. Matthies organizes what they call Fun Dives followed by a barbecue every Saturday, May through October, with additional dives on one or two weeknights. Certified entry-level open water divers can join with experienced divers to explore the pits, which are at least 100 to 200 feet deep, with the largest dropping down to 525 feet.

They can float above an underwater forest and see old fences and railroad tracks, cars and trucks, even building foundations. Combined with the weightlessness of diving, it can feel like gently flying through a hazy underworld, he said.

Another perk: the inquisitive company of sunfish and bass with an occasional appearance of walleye and northern pike that can be up to 3 feet long.

"Sometimes they'll escort you around," Matthies said. "And the loons will occasionally come down and smile at us. It's amazing how sleek they are underwater."

While divers check out the deep pits' watery world, a kayaker may be paddling a loop of mine lakes while a mountain biker carefully zigzags down 200-foot wooded hillsides.

"I look at the Cuyuna area as being a silent sports mecca," Matthies said.

Yet while nature works its magic to reclaim these sites and human creativity makes them more accessible, remnants of industries still whisper their gritty tales.

Lisa Meyers McClintick is the author of the guidebook "Day Trips From the Twin Cities" and the Minnesota Lake Vacations travel app. She blogs at 10000Likes.com.