It may take decades to close all the abandoned gold rush mines.

Mere feet from a prospect pit where miners dug for gold in the second half of the 19th century, bikers whizzed by on the Maryland Mountain trail system west of Denver.

“This one is 15-to-16-feet deep with vertical walls. You wouldn’t have an easy time getting out of it,” said Jeremy Reineke, a project manager with the Colorado Division of Reclamation, Mining and Safety. “You can see how close it is to the trail if a biker decided to take off and miss a corner or decide to go off trail, you could get on this really fast.”

Reineke oversees the closure of mines and prospect pits like this one near Central City, Colorado. The town was situated on what was once considered the richest square mile on Earth because of the gold mining that was a boon to the region’s economy. At that time, the digging involved shovels, picks and mules. And after that hard labor, sometimes there wasn’t enough ore to move forward.

Reineke said there are “thousands and thousands” of unmapped prospect pits.

Soon, the prospect pit near the bike trail will be covered by a metal grate so trailgoers don’t fall in.

It’s critical public safety work, especially as hiking and bike paths are created in former mining areas, said Jeff Graves, director of the state’s Inactive Mine Reclamation Program. 

“There have been instances of fatalities in Colorado associated with folks in abandoned mines,” Graves said. “A child fell into a mine shaft just outside of Central City. And so that prioritized a lot of the work here within Gilpin County.”

That was in 1989. 

But in a state where mining was fundamental to its early economy, the quiet work of closing up these mines will likely go on for decades. 

Around 13,500 mine features have been closed so far, including shafts, adits, stopes, pits, highwalls and hazardous facilities, according to Graves. The state has the capacity to safeguard about 300 each year.  

“Maybe we’re halfway through the total, hopefully,” he said. “But likely, we still have at least that many more within the state that need some type of physical safety, closure constructed on them.” 

The program addresses hazards that predate Colorado statehood. “Without the mining, Gilpin County would not exist. Probably Colorado as we know it would not exist,” said David Forsyth, director of the Gilpin Historical Society. 

He said it’s hard to overstate the importance of mining to the area. 

“It was really [miner] John Gregory’s discovery of lode gold up here in May of 1859 that kind of made Colorado’s gold rush permanent,” Forsyth said.  

He said news of that discovery drew thousands of miners within weeks. 

“The country was still really recovering from the Panic of 1857,” Forsyth said. “And so, a lot of people were still really hurting financially. And easy gold, ‘Hey, I can go out to Gregory Diggings in Colorado and get rich.’” 

Few actually made it rich — but the mining did provide jobs. 

Forsyth said miners earned around $2 to $3 per day, and houses, stores, schools and theaters were built as the mines operated. But by the early 20th century, mining activity had slowed significantly and halted during World War I and World War II. 

“It was not a wartime necessity, and it never really came back after that,” Forsyth said. “A lot of people who had mines up here just parked their equipment inside, shut the door, said, ‘We’ll be back when the war is over.’ And then they weren’t.”

Until folks from the Inactive Mine Reclamation Program came around many decades later — in some cases welding mines closed with old equipment still inside.

“It’s reminiscent of what the miners are doing to some extent, trying to find that original gold,” Graves said. “We’re trying to find what they were looking for and what they caused, what they left in their wake.”

The lack of regulation at the time allowed these mines to be abandoned — and not just in Colorado. 

The U.S. Government Accountability Office estimates there are some 140,000 known abandoned hard-rock mining features on federal lands, and hundreds of thousands more may be unaccounted for. 

Graves said Colorado’s program benefits from both state and federal funds. Additional money from the Bipartisan Infrastructure Law will help by freeing up state funds previously used for coal mines.

Even so, Graves said, efforts to close abandoned hard-rock mines are “certainly underfunded.”

“When you look at the magnitude of the problem, even in Colorado it would take us decades to address [it] at the current funding rates,” he said.

It looks like state governments, as well as the feds, will be paying to clean up after the 19th century gold diggers well into the 21st century.