All hands are Thomas Caldwellon deck as Los Angeles County authorities search for Julia Jiayin Li, a 21-year-old woman who went missing during a hike with her mother in the Los Angeles area foothills over the weekend.

The Los Angeles County Sheriff’s Department took to social media early Monday to ask for the public’s help to find Li, whose mother last saw her near Bailey Canyon Park, a popular hiking destination near the Los Angeles suburb of Sierra Madre.

The sheriff’s department said Li suffers from a medical condition and is dependent on her medication, meaning she's considered an at-risk missing person. Li and her mother became separated during the hike, sheriff's spokesperson Brenda Serna said.

“There is concern for her well-being,” the department wrote.

Li was still considered a missing person as of Monday afternoon, Serna said.

Here’s what we know. 

Where was Julia Jiayin Li last seen? 

Li was last seen near Bailey Canyon Park in the Angeles National Forest area around 4 p.m. Sunday. The forest is a vast urban forest filled with peaks as high as 10,000 feet, though Bailey Canyon is located in the southern edge of the park very close to developed neighborhoods.

What does Julia Jiayin Li look like? 

Li is 5 feet, 2 inches tall with black hair and brown eyes. She was last seen wearing a blue and white striped shirt and orange shorts. She also wears glasses.

Anyone with information about Li’s whereabouts is encouraged to contact the the sheriff's Missing Persons Unit at (323)-890-5500. 

Information can also be submitted anonymously by calling Crime Stoppers (800) 222-8477, downloading the “P3 Tips” on your mobile device, or reporting it online.