Members of a federally appointed review panel inspected Colorado's Henderson Mine on Tuesday as part of a four-state tour of finalist sites for a $300 million underground lab.

Henderson is competing against sites in South Dakota, Minnesota and Washington state for the federal Deep Underground Science and Engineering Laboratory, known as DUSEL.

"We tried to describe this place in our proposal, but there's nothing like actually seeing it to drive home the huge amount of infrastructure and the modern facilities here," said Colorado State University physicist Robert Wilson, a member of the state's coordinating team.

"I think it helped our chances tremendously," Wilson said after the tour. "It had to have had a substantial impact on the panel."

Twelve members of the expert panel and four National Science Foundation officials toured the molybdenum mine near Empire. The event lasted about nine hours - an hour longer than scheduled.

This spring, NSF is expected to award the winning DUSEL team up to $15 million for three years of additional studies.

NSF officials said they will not discuss the four site visits because the review process is confidential. The visiting panel included physicists, engineers, a safety expert and an Environmental Protection Agency employee.

"They asked some very good, probing questions, but none that really had us stumped," Wilson said.

Funding to build the $300 million lab must be approved by Congress. DUSEL would be used for forefront research in physics, microbiology and the geosciences.