(CNN) -- On Sunday night, two teenagers called authorities pleading for help after their hike through the Santa Ana Mountains of southern California went awry.
Then their cell phones went dead -- meaning that not only were they lost, but so, too, was their link to potential saviors.
Their story took a positive turn Wednesday night, when rescuers came across 19-year-old Nicholas Cendoya. But there was no sign of his hiking mate, 18-year-old Kyndall Jack.
Video shot Thursday from helicopters showed Jack perched precariously on a steep area full of dense brush. A rescuer was by her side, and she was hoisted up to an awaiting helicopter and transported to a local hospital.
"She is alive," Orange County Sheriff's Lt. Jason Park said.
Park didn't offer much more than that as he addressed reporters Thursday. He said the teenage girl was "responsive, ... she appears to be dehydrated, she's weak."
But the fact she survived four days in the wilderness was cause for celebration. Park described her family as "extremely happy" upon hearing about her rescue.
There was similar elation among the search-and-rescue team, which included dozens of volunteer sheriff deputies who surveyed the dangerous terrain looking for signs of life.
"Regardless of how hard they worked or how how tired or how hungry they are, it's a tremendous victory for them," Park said.
The ordeal began on Easter, when the two teens set off on trails in part of the Cleveland National Forest located in an unincorporated part of south Orange County.
The pair called the sheriff's department that night, and deputies responded, believing the hikers were about a mile from their vehicle.
"But their cell phone battery died, and contact was lost," the department said in a news release.
That set off a frenetic search through an area marked by dense brush and steep terrain.
A big break came Wednesday night, when Cendoya was discovered, but his hiking mate was nowhere in sight.
"He believed they had been separated possibly since Sunday night and has no recall how they got separated," searcher Michael Boyle told reporters.
Cendoya is being treated at Mission Hospital in Mission Viejo, where Dr. Mike Ritter said he is "awake and talking."
"Nick wanted me to convey to all of you ... how grateful he is for all the help," Ritter told reporters.
As to Jack, Mike Leum with the Los Angeles County Sheriff's Department said he heard her before he saw her Thursday.
"So I was screaming, yelling across the canyon, 'Can you see me?'" Leum recalled. "'Yes I see you,' (she responded), and I could not see her yet, because she was on top of a rock behind a bush."
Leum said he asked Jack to wave the one arm she could, at which point he finally spotted her. By then, a helicopter was on its way -- from which a paramedic at one point descended to check on Jack, and into which she ascended on her way eventually to a nearby hospital.
"She was in a lot of pain, obviously completely dehydrated, and very weak and going in and out of consciousness," said Jim Moss, also with the L.A. County Sheriff's Department. "We just told her not to move because she was in a pretty precarious place."
During Jack's rescue, an Orange County volunteer deputy sheriff "sustained head trauma" after falling 60 feet, the sheriff's department lieutenant said.
The volunteer was in serious but not life-threatening condition at Mission Hospital -- "able to move his arms and his legs ... and he is alert," said Orange County Sheriff's Lt. Erin Giudice.
Orange County Fire Authority Capt. John Muir said one lesson from the ordeal -- even with the happy ending -- is that hikers should plan first and plan for the worst.
"If you're going to go hiking, we want you to be safe, we want you to prepare," he said.