The student was found safe in Cecilville, northwest of Redding, her sister said Thursday.
"There aren't words in the English language to describe the level of relief and elation experienced by [the family]," said Jason Whatley, the family's attorney. "Now begins another hard chapter, but for now, we celebrate."
Tad Cummins, 50, fled with her from their small town of Culleoka, Tennessee, on March 13. They disappeared a few weeks after a student reported seeing Cummins and the teen kissing in a classroom.
A tip led law enforcement to a remote cabin at Cecilville, about two hours from the nearest police station. The Nissan Rogue at the center of the search was parked outside, TBI spokesman Josh DeVine said.
After the capture, one federal charge of transportation of a minor across state lines for the purpose of having criminal sexual intercourse was filed against Cummins, said Jack Smith, acting US attorney for the Middle District of Tennessee. The charge carries a minimum of 10 years.
Cummins is now in FBI custody and will likely make an appearance in the Sacramento Federal Courthouse Monday at 2 p.m.
A 2,000-mile escape
Surveillance video showed the pair at a Walmart in Oklahoma City on March 15. But after that, the trail went cold.
The break came when someone spotted Cummins in a remote part of Siskiyou County, California, more than 2,000 miles from Culleoka, and called the Tennessee Bureau of Investigation tip line.
The caller said he had taken up residence in a remote cabin in Cecilville, DeVine said. The TBI earlier had said the two were found in a commune, but later backed off that description.
Siskiyou County deputies searched the area and found the vehicle. They confirmed through the VIN number that it belonged to Cummins, Devine said.
Deputies monitored the car and took Cummins into custody as daylight broke, said DeVine.
The teen was found "healthy and unharmed," TBI Director Mark Gwyn said. Arrangements are being made for her return home. The main concern is for her emotional well-being, Gwyn said.
"As we have said from the start, it only takes one tip," Gwyn said. "This is yet another example of the value of the public helping us to rescue a kidnapping victim."
Cummins faces charges of sexual contact with a minor and aggravated kidnapping, the TBI said last month.
But state law allows children older than 12 to decide whether to leave their families, unless their removal or confinement "is accomplished by force, threat or fraud."
That means to prove a kidnapping took place, prosecutors will have to show she was unlawfully removed or had her freedom restricted.
Estranged wife speaks out
Cummins' estranged wife, Jill Cummins, was "very emotional" when she learned both were found safe, her attorney Michael Cox said.
"She is excited that they were found and nobody was hurt," Cox said. "She has not spoken to Tad."
Jill Cummins had filed for divorce, saying she felt betrayed by her husband. She had no idea why her husband went to Northern California.
"This is not somewhere they had frequently visited," her attorney said. "I'm not aware that they had ever been there."