Driving past the Unimin plant on Le Sueur County Road 23 near Ottawa, the enormity of the mining operations going on is not apparent.

But take a ride with plant manager Grey Lusty around an earthen berm and down a bumpy gravel road, and the scene that opens up is similar to the gold mines of Lead, S.D., or the coal fields of Wyoming.

Giant 100-ton trucks, loaders and other heavy equipment scuttle around a broad, deep terraced mine.

At the lower portions of the 170-foot deep pit is the prize -- fine white silica sand.

The largely unnoticed local company is indicative of an industry that draws natural resources from the ground in and along the Minnesota River Valley. Often operating in out -- of-the way areas, the plants -- and their significant economic impact -- are often overlooked.

"I'm still a little surprised when I tell people who I work for and they don't know who we are or what we do," Lusty said.

The geology of the valley makes it prime for mineral extraction. Some of the oldest granite in the world is upstream. Hard dolomite, sandstone, clays, gravel and other minerals are all along the valley. But it was a horrendous natural event 10,000 years ago that made the area's mining industry what it is today.

Glacial lake Agassiz, which covered a large part of northern North America, broke open sending torrents of water, over hundreds of years, digging out the deep Minnesota River Valley.

That event makes it economically feasible to get to the minerals that would otherwise be too far underground to access.

Unimin: Modern face of mining

The various grades of Unimin sand are used in four industries: glass making, the back dusting on shingles to keep them from sticking together in the pack, the making of molds in foundries, and extraction of oil and natural gas.

Lusty, who's been with the international mining company for 15 years and at the local Unimin mine since 2000, said the entire Kasota operation is geared toward sand for the oil and natural gas industries.

" The pure, hard grain and because it is round is what makes our sand so desirable." Companies use the sand to extract oil and natural gas from wells that no longer produce well with normal pumping. The sand is pumped down the wells and forced into the veins, fracturing them. That expands them and the sand remains in the veins, holding them open while oil flows out. That's where the strength and roundness of the sand is vital, Lusty says. It's strong enough to hold the veins open and the oil can flow through the round grains of sand because they don't compact.

Recent high oil prices sent oil companies back to less productive wells, boosting the demand for the silica. The Kasota plant is operating seven days a week, 24 hours a day. Unimin has 75 employees and has a broad indirect economic impact in the area. "All the contractors and vendors who we work with in the area produce a lot of economic activity. We have a big impact on a lot of people around the area," said Lusty, a Montana native whose father was in the gold mining industry.

Stones for the world

While most area mining operations go largely unnoticed, the limestone quarried between Mankato and Kasota is well known, not just locally but across the nation and around the world.

The local stone is being used on the new Twins stadium, was used to cover the dramatic curved architecture of the Smithsonian's American Indian Museum in Washington, D.C., used on the American embassy in Moscow, and in numerous government buildings, including the Mankato post office.

"Limestone occurs almost every place in the world," said Howard Vetter, of Vetter Stone. "But in very few places does it have the quality and the strength and freedom from cracks and defects that allows large pieces to be cut from it."

As it turns out, the shelf of limestone between Mankato and Kasota is of extremely high quality and a variety of colors. And because the glacial waters carved the river valley down to the limestone, it's accessible to Vetter and his children, who are the third generation to operate the quarry.

Vetter Stone also owns and operates an Alabama quarry that provides limestone with charcoal- colored veins over a light colored background.

While access to gravel deposits and silica sand in the area will become more and more limited in the coming century, Vetter has a 500-year supply of good limestone locally. The Alabama quarry has a 2,000year supply.

Vetter, who has 80 employees in Minnesota and 45 in Alabama, said the family works hard to keep up with technology. "We have avery modern facility and always look to upgrade. It's changed a lot. My father died in 1975 and there are no machines from that era we still use."

Gravel tougher to get

When it comes to mining, there is nothing more common, widely used and necessary than gravel and crushed rock.

But accessing aggregates is becoming increasingly difficult and expensive, adding to the cost of everything from road projects to building a driveway.

"It's getting a lot harderto get permitted. The requirements are a lot more stringent with the air and water regulations," said Eric Leverson, general manager of construction at Southern Minnesota Construction.

"In a lot of places, usually near urban areas, it's impossible to get permitted at all." The regulations came about in large part, he said, because the complete lack of regulations in the past led to problems.

"Years ago you opened a gravel pit and did whatever you wanted. So it's not a bad thing that there are more regulations."