A 50-year-old woman went missing Sunday after going for a hike and leaving her group behind at Black Mountain Open Space Park in Rancho Peñasquitos.

San Diego police said the woman, Diem Le Nguyen, continued up the Nighthawk Trail alone, going ahead of her hiking group after they stopped halfway up around 8 a.m. She made contact with the group around 9:30 a.m. to say she was “at the end of the trail” but was not seen after that.

Police put out an alert on social media shortly after 2 p.m. indicating they were searching for Nguyen.

By 3 p.m., sheriff’s helicopters, members of a search-and-rescue team and San Diego police continued to look for the missing hiker.

Last seen wearing a black shirt with a pink heart on the front, black pants, a brown hat and sunglasses, Nguyen is about 5 feet tall and weighs about 105 pounds. She wore a backpack during the hike.

The hike occurred as hot conditions enveloped the San Diego region Sunday. The National Weather Service had issued a heat advisory for the valley areas of San Diego County through 8 p.m., with temperatures reaching 91 at Miramar and 90 in Rancho Bernardo.