Jennifer Ackerman and seven friends hired a driver to take them to the STS9 concert at Red Rocks on Saturday night because they wanted to be safe.
But as the band played its last encore before a sold-out amphitheater early Sunday morning, Ackerman and others standing in the stairway at the foot of the formation known as Creation Rock suddenly heard a loud noise.
“It sounded like an explosion,” Ackerman’s cousin, Stephanie Wiser, said Monday.
The sound actually was a large boulder and several other pieces of rock falling from Creation Rock on the north side of the amphitheater and onto the crowd below.
Before they knew what had happened, another Ackerman cousin, Jancy Polzkill, saw Ackerman lying face down, a gash in her head and blood flowing from her face.
Ackerman was among seven people injured when rocks fell on the crowd — something that hasn’t happened at Red Rocks Amphitheatre in more than two decades.
On Monday, city officials brought in a private contractor that specializes in rock stabilization to investigate what may have caused the rocks to fall.
Kristin Rust, a spokeswoman for Denver’s Office of Cultural Affairs, said authorities have received unconfirmed reports of people climbing on the rocks in that area — a violation that can result in a $999 fine. Security will monitor Creation Rock for the rest of the year to prevent any climbing.
It was still unclear, however, what caused the rocks to come tumbling down, she said.
“We may never know,” Rust said.
The injuries occurred about 1 a.m. Sunday.
At least a half-dozen rocks fell on people on the north stairway, approximately between rows 20 and 40. Four of the seven injured were taken to the hospital.
Ackerman, a 34-year-old mother of two from Westminster, had the most serious injuries.
She was standing near row 20 when a rock hit the top of her head, leaving a gash that required 14 staples, Wiser said. She fell face-first onto the steps, fracturing facial bones and chipping several teeth.
Ackerman was stable in intensive care at St. Anthony Hospital on Monday afternoon. She was coherent and communicating but had some bleeding on the brain, Wiser said.
Denver native Wiser, who attends many concerts a year at Red Rocks, described the incident as both surreal and “sobering.”
After the amphitheater had cleared out, she saw the large boulder, which was at least a foot tall and had come to rest near the fifth or sixth row. Had that rock hit someone or if the rock that hit Ackerman had struck her in the temple, the injuries could have been deadly, she said.
“The ‘what ifs’ are really scary.”
Staff writer Joey Bunch contributed to this report.
Sara Burnett: 303-954-1661 or sburnett@denverpost.com
