There's no estimate yet on when Red Mountain Pass near Ouray will reopen.
U.S. 550 was closed in both directions Monday because of a long-lasting rock slide.
The Colorado Department of Transportation says rocks began tumbling onto the road Sunday evening, and by Monday the rock fall was described as continuous. A rock fall contractor is expected to inspect the pass Tuesday morning by helicopter and on the ground.
Rocks up to 6 inches in diameter are covering about 200 feet of highway, and a pile 8 feet deep formed at one spot. Rocks also severed a power line.
CDOT spokeswoman Nancy Shanks told The Durango Herald that the slide is probably the result of a deep freeze-and-thaw process, which she said is unusual for this time of year.