Investigators have not identified a reason for the rock fall at Red Rocks Amphitheatre that injured seven people at a concert by Sound Tribe Sector 9 after midnight on Saturday.
Four people were taken to hospitals after seven were hit by rocks that fell from Creation Rock on the north side of the amphitheater about 1 a.m. Sunday. The monolith is 300 feet tall.
There were unconfirmed reports of people climbing illegally on the rocks in that area, which can trigger a $999 fine.
The rocks came down between rows 20 and 40.