The 17-year-old girl who fell is still recovering, Denver Police spokesperson Sonny Jackson said.
Police and Denver Fire officials responded to a report of a girl falling about 45 feet from the roof of the building to the floor around 5 p.m. Sunday.
She was taken to the hospital. She did not have life-threatening injuries, but may face a long recovery, Denver Fire said.
"I don't think she'll ever be, what she was before," Denver Fire spokesman Lt. Phil Champagne said. "She suffered such traumatic and serious injuries."
Champagne did not elaborate on the injuries.
The three boys along with the girl now face trespassing charges, Jackson said.
The Denver Fire Department had to force their way into the building. The building is abandoned, and police are not sure how the teens gained entry.
Demolition and redevelopment on the property began four years ago, but the process has been stalled by environmental delays and economic factors.
The site continues to be an attraction for urban explorers.
"It's a bit of a rush," said Urban Explorer Zachary Byron Helm, who has been in the building eight times since it was abandoned more than 10 years ago.
But he recommends staying out of the building because of the constant police presence.
"It's not fun to be caught," he said. "It's not fun to go to jail especially for something as silly as walking around a building and taking pictures."
Gates produced rubber products at the Denver site for 85 years before moving its manufacturing elsewhere.
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