The person flagged down a motorcycle deputy, who found the big cat in the Macy's parking lot. Temecula police also responded and contained the animal. The mall was not open at the time.
California Department of Fish and Wildlife officers arrived at about 7 a.m. and tranquilized the animal.
The full-grown male puma died during transportation back to the nature preserve, wildlife officials said.
The 150-pound animal was turned over to a biologist for necropsy.