PHOENIX – Devoid of signs or barriers, the derelict mine shaft was so well-hidden that rescuers searching for two sisters walked right by it in the darkness.
But in the light of day Sunday, they were finally able to see the tracks of an all-terrain vehicle leading into the shaft, a 125-foot vertical drop into a chamber where one of the girls was trapped overnight with her sister's body.
Rescuers who rappelled to the bottom of the northwestern Arizona mine Sunday found 13-year-old Rikki Howard dead. Ten-year-old Casie Hicks was listed in critical condition at a Las Vegas hospital Monday.
"A 10-year-old girl has spent the night at the bottom of a mine shaft, which is the most horrifying thing I can think of," Capt. Greg Smith of the Mohave County Sheriff's Office told reporters.
The girls' relatives were at the hospital Sunday evening and declined to comment.
The girls and their dad had been out riding for fun Saturday night in Chloride, about 200 miles northwest of Phoenix.
"They were having a holiday weekend jaunt riding ATVs in the mountains there," Smith said.
Their father was riding ahead of them on his dirt bike when he noticed they were no longer behind him.
"[The girls] were driving along and they went into the mine. It was a total accident," Mohave County Sheriff's Department spokeswoman Sandy Edwards said.
Rescuers searched throughout the night, but Edwards said the rough terrain and darkness were too much.
"During the night, our team walked by the site because the hole itself was hidden by this line of brush," she said.
When the girls' father yelled into the gaping hole, only one daughter answered.
Seth Johnson, a neighbor of the girls and their family's landlord, said the two were half-sisters. "It's an awful shock," he said. "Their parents are very distraught."
Cathy Kelso, a bus driver, said she has been driving the two girls to school for a year and a half. "They're little sweetheart girls," she said. "I just keep hoping it's not true, but it's horrible."
The mine shaft the girls fell into is like thousands of others throughout the state that are unmarked and open, officials say.
"There's a significant amount of abandoned mines out there that are hazardous to the public's health," said Laurie Swartzbaugh, deputy director of the Arizona State Mine Inspector's office.
Swartzbaugh said the Chloride mine had not been used for some time, and that the office was investigating. The office has secured 108 abandoned mines since Jan. 1.
It was not immediately clear who owned the mine. Many abandoned mines date back to the early 1900s and it is sometimes impossible to determine who owns them.