COLORADO SPRINGS, Colo. -

An autistic man from Colorado Springs is lucky to be alive after wandering the Utah desert for three weeks with little food or water.

William LaFever, 28, was rescued Thursday after surviving on frogs, roots and river water in the Escalante desert.  Officials said he probably wouldn't have made it another 24 hours had he not been found.

"God and time and everything were on our side yesterday, and I just can't imagine had it gone another day," said Lisa LaFever, William's sister.

Lisa said her brother, an experienced hiker and outdoors man, had spent a long time planning a hiking trip from Utah to Arizona. But things went wrong -- William's camping gear was stolen and he ran out of money.

Lisa said the plan was for William to find a ride to Arizona so her dad could wire him money. But even without his supplies, William decided to keep hiking. His rescuers said he walked roughly 50 miles.

Lisa reported her brother missing on July 7.

"As more time was going on, the sheriff's office wasn't as hopeful, and I think that was very hard on us," said Lisa.

On Thursday, Utah Highway Patrol Helicopter Pilot Shane Oldfield spotted William. He had collapsed from weakness.

"Just having sat up to be able to wave his arms was probably a feat for him,” said Oldfield. “The fact that he was alive at all was incredible, and that he was conscience, cognizant and coherent was miraculous.”

Lisa said her brother's autism has always made him very focused and determined, and she believes those qualities are what kept him alive.

"I think that's what got him to survive because he was so dedicated, and he didn't want to give up," said Lisa.

William is now recovering at a Utah hospital. Lisa said he's feeling a little overwhelmed because his story is getting media attention across the country. She said he is focused on getting better, and it's not clear when he may be able to come home to Colorado Springs.

Lisa said she's seen some criticism of her family for allowing William to go hiking alone. She said her brother lives on his own, despite being autistic, and while she and her parents weren't happy with his plan, they had no choice but to let him go.

"He wasn't abandoned by his family, "said Lisa. "This is something he really, really wanted and we supported him. Things just didn't go how they needed to go, unfortunately. But thank God he was found and thank God he's betting treatment and getting better."