An Arizona jury on Wednesday found a man guilty of child abuse for forcing his grandsons on grueling hikes in the Grand Canyon in searing August heat even as the boys threw up and two of them repeatedly fell because of cramping.

A 2006 file photo provided by the Indianapolis Metro Police Dept, shows Christopher Carlson, who was found guilty of child abuse for forcing his young grandsons on two long hikes in in the Grand Canyon hiking trail and denied them water and food. (Indianapolis Metro Police Dept, file/ AP photo)

The jury found 45-year-old Christopher Alan Carlson of Indianapolis guilty of three of six charges of child abuse stemming from the hikes on Aug. 15 and Aug. 28, when his three grandsons were 8, 9 and 12. Each hike lasted at least 24 kilometres.

Carlson could face life in prison when he is sentenced June 1.

All three boys testified during the trial, which began Feb. 15.

The oldest described secretly asking a hiker to call 911 toward the end of a roughly 30 kilometre hike on Aug. 28 after he started throwing up, falling down because of cramping, experiencing changes to his vision and hearing and became scared.

All the boys said that Carlson pushed, choked and kicked them during the hikes.

"I needed medical attention and I was hurting and he was hitting and pushing me and calling me fat," said the boy, who is still 12 years old. "I was scared and it was hard and I was all weak and tired and kind of hurt."

Prosecutors told jurors that Carlson deprived the boys of food and water during the hikes. The boys reported that they did get some water, but not always enough, and ate celery and other snacks during the hike.

A criminal complaint said Carlson put his grandsons in circumstances "likely to cause death or serious bodily injuries."

Investigators have said that Carlson told them that the boys were overweight and that he thought hiking the Grand Canyon would help get them into shape.

Defence attorney Jeffrey Williams has portrayed Carlson as an active health nut who had a firm hand and wanted to show the boys the world. Like anyone after a long hike, the boys were tired, hungry and thirsty, but Carlson only allowed the boys to eat healthy food like tofu, hummus and veggie burgers, Williams said in his opening statement.

Carlson is such a young grandfather because he was 15 when he had his first child, a girl. His daughter, Tara Danaher, was also young when she had her first child, the oldest of the boys, at 17.