The mountain lion sighting was first reported at 6:40 a.m. on Walnut Avenue, between Baseline Road and Allen Avenue, according to the Los Angeles County Sheriff's Department.
Deputies and California Department of Fish and Wildlife personnel arrived at the scene, just north of the 210 Freeway, and located the animal sitting under a tree alongside Foothill Boulevard.
At 10:30 a.m., video from AIR7 showed the mountain lion occasionally wagging its tail as authorities closed the nearby street and set up a perimeter.
"Please avoid the area this morning until the mountain lion has been safely relocated," the sheriff's San Dimas station said in a social media post that included close-up photos of the animal. "Residents in the area are encouraged to secure all pets and remove or secure any outdoor food that could attract wildlife to residential properties."
Despite warnings from authorities, at least two dozen curious onlookers arrived at the scene to watch the incident unfold.
Sometime after 11:00 a.m., a wildlife official with a compressed-air tranquilizer rifle fired at least two darts at the mountain lion, who was struck by one of the syringes and used its mouth to pull it out of its body. The animal then chewed on it for a moment before spitting it out.
Around 11:30 a.m., several officials approached the sedated animal and picked it up with a transport tarp and carried it to a waiting vehicle.