An Indiana man was in court Thursday to face charges of endangering the health and safety of his three young grandsons by allegedly abusing them physically and verbally and denying them water and rests on a 19-mile hike into the Inner Gorge of Grand Canyon National Park during one of the hottest days of the summer, according to a sworn complaint filed in U.S. District Court.

The 24-page complaint against Christopher Carlson, of Indianapolis, details numerous instances of physical and verbal abuse against the boys, aged 12, 9 and 8 years old.

Mr. Carlson, during his interview with rangers, denied commiting any physical abuse, the complaint noted.

The complaint submitted by Special Agent Christopher Smith was built around information provided by rangers who encountered and observed Mr. Carlson and the boys on the Bright Angel Trail on two separate occasions, August 15 and August 28. Rangers also were contacted by another hiker who encountered the four on the Bright Angel Trail on August 28.

The caller told rangers that the boys "were hyperventilating and one of the children told the caller 'call the agency' or 'call the emergency,'" the complaint noted. "The description given by the caller matched Carlson and the boys."

Among other allegations contained in the complaint:

* A law enforcement ranger on the South Rim who watched the four on the Bright Angel Trail through binoculars "saw Carlson shove John Doe 1 thirteen times. Of those thirteen times, four appeared to occur when the boy tried to stop and rest. Ranger Blair also witnessed Carlson whip John Doe 1 with a rolled up tee shirt. When John Doe 1 was struck with the shirt he lurched forward."

* After the four reached the top of the trail, rangers separated them and talked to the boys, who said they were "hit, pushed, choked, kicked, pinched, squeezed, and whipped. They said they were not allowed to drink water on the hike down and resorted to drinking water from the Colorado River. Overall, all three relayed to Ranger (Elizabeth) Aurnou they were afraid of Carlson, did not want to be placed back in his care, and felt he should be arrested."

* On the August 28 hike, which covered roughly 19 miles, temperatures at Phantom Ranch on the floor of the canyon reached 108 degrees, and another park visitor died that day from heat exposure on the Tanner Trail elsewhere in the park.

* While being examined August 29 at the Safe Child Center in Flagstaff, Arizona, John Doe 1 told authorities that during the August 28 hike down the Bright Angel Trail the boys  "were not allowed to drink any water until Carlson said they could, and the boys had no water until they reached Phantom Ranch. When they would ask Carlson for some water, he would say no, then drink some water himself in front of the boys."

* During the return hike to the top of the South Rim, John Doe 1 said Carlson gave him and his brothers some water, but they all vomited after drinking.  "Carlson then told them they would not get any more water until they got to the top of the trail.  He (John Doe 1) threw up three times on the hike, John Doe 2 threw up twice, and John Doe 3 threw up five or six times," the complaint alleged.

* While hiking up the trail, John Doe 2 said his legs would cramp so badly that he kept falling down. "This would anger Carlson, who would then choke him and pick him up by his throat. Sometimes Carlson would pick him up by the throat and then throw him to the ground," the complaint alleged.

Other allegations contained in the complaint indicated some of the boys were suffering from heat stroke during the hike on August 28, alleged that the grandfather would kick and push the boys down onto rocks, throw rocks at them, choke them, deny them water, and used abusive and disparaging language.

The grandfather also allegedly told the boys they "better have smiles on their faces when they pass people, act happy, and say 'Hi.'"

Medical examinations of the boys detected a number of injuries ranging from lacerations and bruises to contusions and general dehydration, the complaint noted.

No details were provided as to the current location of the boys or where their parents were.