Miyuki Harwood, 62, failed to return from a solo hike on 21 August and fellow hikers alerted authorities.
Foot, helicopter and drone searches had failed to find her but she was finally located near Courtright reservoir in Fresno County on Saturday.
Rescuers said she had suffered broken bones but was conscious and "very grateful" to be found.
California Highway Patrol flight officer Rusty Hotchkiss told reporters: "She was really at the end of the time period when we thought she could survive."
He said Ms Harwood had heard nearby rescuers on Saturday morning.
"She heard them talking, she heard voices and she grabbed a whistle she had with her. That alerted the rescuers to find her," Mr Hotchkiss said.
He said she had crawled for two days down to the creek.
Ms Harwood, from Orangevale in California's Sacramento County, has been taken to hospital for treatment.
She had reportedly had no food and had been drinking water from the creek using a water filter.
The rescue effort had been hampered by smoke from a wildfire in the Kings Canyon National Park.
An American hiker missing for nine days in California's rugged Sierra Nevada has been found alive.