The Colorado Division of Reclamation, Mining and Safety (DRMS) oversees the safeguarding and closing of abandoned mines.
It estimates there are about 23,000 abandoned mines statewide, and so far, 6,127 have been closed.
"Abandoned mines will kill you," Matt Collins, a mining engineer and adjunct professor at the Colorado School of Mines, told Denver7. "I remember closing mines 20 years ago, and here we are, we're still closing today so it's gonna be a long process."
Collins is trained to perform rescues and said the dangers of old mines are never worth the risk.
"Biggest risk is the big three -- falling, number one; having the ground fall on you; and then bad atmosphere."
He said the message is simple: Stay out, stay alive.
"If you see a hazardous opening like this at all, contact the Colorado Division of Reclamation Mining and Safety, they'd be happy to close it," Collins said.
DRMS said it receives, on average, $2 million each year for mine safeguarding work. The average cost of each closure is about $5,000.