Over 42 years, a massive hole is next to Umstead State Park. How Triangle Quarry works

Just off Interstate 40, near the Reedy Creek entrance to William B. Umstead State Park, is a hole in the ground so deep that someone standing at the bottom is 180 feet below sea level.

The Triangle Quarry opened in 1982 and has provided crushed stone to countless construction projects in one of the country’s fastest-growing regions. If the tallest building in Raleigh, the 33-story PNC Plaza, were placed inside the 500-foot-deep hole, only the building’s crown and spire would be visible.

Now the quarry is nearing the end of its life. Wake Stone Corp. has slowed production, and president and CEO Sam Bratton estimates it has about five years worth of stone left before the quarry is played out.

The company wants to extend the life of its operation here another 25 to 35 years by digging another hole on adjacent land owned by Raleigh-Durham International Airport. Stone from that quarry would be trucked across a new bridge over Crabtree Creek and processed on the Triangle Quarry’s existing machinery.

The stone from the Triangle Quarry is a light gray, granite gneiss, prized for its rigidity and durability. Once a mining company has found a good deposit and removed the trees and soil on top, the process is pretty simple: Drill holes in the rock, load in explosives, blast, then scoop up the loosened rock and truck it to a machine called a jaw crusher.

A winding road hugs the quarry wall on a gradual ascent from the floor to the rim. There are no guardrails, but the road is plenty wide to accommodate the mining trucks that are more than twice as wide as typical dump trucks and can haul up to 70 tons of rock at a time, at 15 mph.

About halfway up the road, on a wide ledge off to the side, is the Triangle Quarry’s primary crusher. It takes big chunks of rock and breaks them into 9- to 12-inch pieces, which ride a conveyor belt up to the top.

There, another series of crushers makes smaller stones, which are screened and sorted into different products, from rocks used for rip-rap and railroad beds to dust and fine pebbles that go into pavers and concrete block. Other grades go into concrete or as gravel beds for roads and buildings.

About 200 people work at the quarry. For about every 40 hours that workers crush and sort rock, they spend another eight to 10 hours fixing and maintaining the machines, Bratton says, as he drives his Chevy Silverado up from the pit floor.

“This is a very tough environment, and you get a lot of wear,” he says. “There’s greasing; there’s steel that’s wearing out. Lot of welding that’s done. There’s always maintenance to be done.”

Trucks owned by contractors and construction companies collect the sorted and washed stone and haul it out onto North Harrison Avenue and I-40. Bratton said Wake Stone is one of the last stone companies that also allow somebody to drive in with a pick-up truck or a trailer and get a load.

“No sale is too small,” he says.

Wake Stone pumps water from the Triangle Quarry to a small reservoir at the top, where most of it is used for washing dust from stone before it leaves the yard. That water is mostly from rain that falls into the pit and doesn’t drain. Powder from the rocks gives the water a blue-green tint like that of a glacial lake.

Crabtree Creek snakes along the perimeter of the quarry, but no creek water gets in, says Cole Atkins, Wake Stone’s head geologist, and very little groundwater seeps in from the sides.

“This rock is very, very tight,” Atkins says. “There’s not a lot of fracturing.”

If and when Wake Stone begins mining on the RDU property, it will make the topsoil available to customers. Otherwise, it will dump it into the Triangle Quarry, which will also begin to fill with water. Wake Stone will keep an eye on the water levels and pump out water before it reaches the jaw crusher on the ledge, which will be the first stop for the RDU stone.

In a green, tree-covered part of the country, a stone quarry looks out of place, like a harsh, dry landscape found out west. As workers blast rock deeper into the quarry, each layer is slightly smaller than the last, creating a series of steps along the quarry wall that help keep it stable. Trees sprout along the narrow ledges.

“You can tell by the color, they’re not the healthiest,” Bratton says. “That’s a pretty tough spot to grow. Nothing but rock.”