'Their lives are in danger': Family desperate to find mom, 11-year-old daughter who vanished in California

An Oklahoma woman with bipolar disorder and her 11-year-old daughter have vanished in Southern California -- and their father and grandfather are desperate to get them home safely.

Amanda Kay Key, 40, and her daughter Haley Marie Vilven were last heard from on September 16, possibly near the El Monte bus station in Los Angeles County, said Key's father, Steven Jindra.

"Their lives are in danger," he told ABC News.

Jindra, 66, said his daughter and granddaughter had lived in Texas, but Key was then promoted and the two moved to Tulsa.

Once in Tulsa, Key lost her job and apartment, he said, but then she landed an interview in California so the two drove out there.

Jindra said he and Key spoke on September 15 while she was near the El Monte bus station in Los Angeles County, but then "we miscommunicated on how to get the money to her. She was running out of money and she was gonna catch a bus and take it to Houston."

"She ended up not getting the money and by Sunday she was despondent," he said. "And Sunday evening she borrowed a man's phone and sent a text, and it was clear from the text she was very despondent. It sounded like she had a breakdown."

Key has bipolar disorder, according to her father and the Los Angeles Police Department.

The text conversation that Sunday "was the last communication we've had from them," Jindra said. "No friends or family or any of her supporters have heard a thing."

"My biggest worry is she had a breakdown ... I'm afraid she might be out somewhere in the El Monte area, maybe out in the woods," he said. "I'm real sure she's in a mental state right now and their lives are in danger."

Jindra said the two likely are walking on foot with luggage. He's begging for anyone who may see them on a path, or at a park, to call the police.

"I'd like people in El Monte to really look at the pictures and see and think if they've seen them," he said.

The concerned father and grandfather said he hopes to "take them back to Houston and get them home and cared for. That's the main thing."

Key is described as having brown hair and brown eyes. She is 5-feet-7-inches tall and weighs about 160 pounds, police said.

Haley also has brown hair and brown eyes. She is 4-feet-10-inches tall and weighs about 100 pounds.

Police ask anyone with information to call the LAPD's Missing Persons Unit at (213) 996-1800.