Image caption The Escalante River ends in the man-made Lake Powell

An autistic man who survived for three weeks in a remote Utah desert is said to be in a stable condition.

William Martin LaFever, 28, travelled an estimated 40 miles (64 km) in the Escalante Desert in southern Utah, in an attempt to walk to Page, Arizona.

Mr LaFever told his family that his hiking gear had been stolen, and his father had wired money to Page.

To survive, he scavenged food, including frogs, and drank water from the Escalante river.

Deputy Ray Gardner, who was aboard the helicopter that spotted Mr LaFever, said the 28-year-old was emaciated and could not stand when he was found.

"I could not believe that he was alive, and feel certain that in another 24 hours he would not have been alive," Mr Gardner said in a statement.

A sheriff's office said that Mr LaFever had called his father in early June to say he was hiking in the area with his dog, but that some of his hiking gear had been stolen and he was out of money.

John LaFever, of Colorado Springs, Colorado, told his son to catch a ride to Page to get the money.

Instead William LaFever apparently decided to hike along the Escalante river and then hitch a boat ride along Lake Powell to the Arizona town, according to the sheriff's department.

Garfield County Sheriff's spokeswoman Becki Bronson told the Associated Press that the desert is "some of the most rugged, unforgiving terrain you will find anywhere on Earth", including "jagged cliffs, stone ledges".

"Where William was hiking, there just isn't anyone out there," she said. "There are no people. There are no towns."

Mr LaFever was flown to Garfield Memorial Hospital, and Ms Bronson told the BBC he is in stable condition.