Kennecott has informed investors it will produce 140,000 fewer tons of copper in 2013. It had planned to move 260 million tons of rock from the pit, but faces a waste pile nearly as large.

Company officials were uncertain how much of a cleanup was necessary — they could leave some of it in place and work around it.

Kennecott officials say two crucial pieces of equipment — a rock crusher and conveyer belt — were left undamaged inside the pit, making a faster recovery possible. They said federal regulators had granted them access to the bottom of the pit only Thursday.