(Image Credit: Courtesy Fresno Sheriff's Department)

ABC News' Lawrence Dechant reports:

A 64-year-old hiker who became stranded after taking a wrong turn and spent more than two days clinging to a sheer cliff face in California's Sierra National Forest said his strength was slipping away and that the rescue team came just in time.

Before being rescued Saturday, Lawrence Bishop had fallen into despair and had begun hallucinating.

"I've never been in position to say, you know, 'How much am I willing to do to stay alive?'" Bishop said Tuesday. "I basically stayed awake all night and wrote a goodbye letter to my wife and daughter."

The experienced hiker had gone climbing with friends. He was separated from them Thursday, and they reported him missing the next day.

Bishop said he had seen some children on top of Dog Tooth Peak and he climbed it, took photos with them and started down.

The peak is composed primarily of granite. As he was working his way down, he slipped, fell backwards and hit his head, he said.

The 10,000-foot descent was steep and perilous, and he couldn't negotiate the smooth, slick granite plates.

"I just basically hoped I had the stamina and determination to bear the pain and hang on," he said. "I said, 'I can't get down this.' I found a little hole in the rocks and I planted my butt there and my poles into the granite plates, and I anchored myself and thought, 'Either I am going to get rescued or I am going to die here,'" he said.

Bishop said he had no water and ate plants to survive. As the hours lingered on, he attempted to rest.

"Friday, I despaired of anybody seeing me, so I tried to inch down to a spot where I could sleep better, skinned up my left side, my butt and right arm and elbows got torn up," he added.

A total of 52 hours into his ordeal, Fresno County Sheriff's Office rescuers finally arrived. By the time they made their mad dash to Bishop, he didn't think he could hold on much longer, and his rescuers didn't think so, either.

Search and Rescue team leader Russ Richardson and Fresno Sheriff's Department Det. David Rippe risked their own lives to sprint several hundred feet up the slick rock. From there, a helicopter was sent to take Bishop down the mountain.

Bishop now says that even though he thought he would die, he made it for a reason.

"I wasn't done living yet," he said.