A giant sinkhole that caused part of a highway near the top of a Colorado mountain pass to be shut down earlier this week was caused by thawing soil in an abandoned, century-old railroad tunnel, engineers there said.
The Colorado Department of Transportation was forced to close part of U.S. 24 between Red Cliff and Leadville after the 100-foot-deep, 20-foot-wide sinkhole was discovered near the top of Tennessee Pass.
