The boy was hiking with 10 other people at the Rancho Peñasquitos Canyon Preserve when the attack occurred around 2:30 p.m. Witnesses told KGTV that the boy's father kicked the big cat and threw a rock at the animal to scare it away. It was not clear what, if anything, provoked the attack.
When officers with the California Department of Fish and Wildlife arrived at the scene, they found mountain lion tracks.
The animal was "dispatched" when it approached some of the officers displaying no fear, the agency said in a statement.
“The lion appeared to have little fear of humans, which is abnormal behavior for a mountain lion,” the CDFW said.
The boy was treated by San Diego Fire-Rescue personnel and taken to a hospital with a non-life threatening injury.
"The 4-year-old boy is in good condition, recovering well from his injuries and expected to be released from the hospital soon," Carlos F. Delgado, a media relations officer for the Rady Children’s Hospital, told Fox News affiliate KSWB-TV.
Samples of the boy’s clothing and the lion's carcass were sent to wild forensics specialists in Sacramento to confirm that the lion killed was responsible for the attack.
The Los Peñasquitos Canyon Preserve encompasses 4,000 acres of open space with 37 miles of trails. Trails within the preserve were closed following the attack for an unspecified amount of time, KSWB reported.