Utah's largest coal operator, St. Louis-based Arch Coal Inc., turned away from a deep coal seam at the Dugout mine in central Utah, leaving behind 4 million tons of coal a year ago.

McCarter and other mining experts question whether regulation has gone too far.

Mining authorities ordered a new method of longwall mining that effectively cuts West Ridge's reserves in half, "and I'm not really sure anybody has proven it any safer," McCarter said.

The cave-ins are part of everyday deep mining, McCarter said. Two common methods of coal removal, longwall and retreat mining, depend on orderly, controlled cave-ins for safety.

But federal officials say the size of the Crandall Canyon disaster showed more scrutiny was needed.

"In the past, anything an operator submitted — if it was a reputable operator — we took their word for it," Stricklin said.

Others agree the tighter regulations are a welcome change, because mining companies for years got a free pass.

"It was a rubber stamp," said Mike Dalpiaz, the mayor of Helper and a United Mine Workers of America vice president. "We had to spill blood before they started paying attention."

Miners are paid well for the dangerous job — around $65,500 a year, double the region's average wage, according to the Utah Department of Workforce Services

About 4,000 feet inside Horizon via a honeycomb of sloping tunnels, Dallen McFarland used a cable-connected joystick to finish boring a tunnel with a 50-ton cutting machine.

He didn't flinch when the walls — miners call them ribs — started making noises like a knuckle cracking, with the weight of 800 feet of mountain cover bearing down.

"When your ribs are popping, that's good because it means they aren't storing energy," McFarland said.