The state Department of Fish and Game has offered a $2,000 reward, the Los Angeles Times reported.
A driver called in a report of an animal on Highway 101 near Buellton in Santa Barbara County early Tuesday morning. A California Highway Patrol officer who found the carcass moved it off the road and out of the sight of passing drivers and called Fish and Game to report the death at about 5:30 a.m.
The investigator who arrived at 9 a.m., Lt. Jim Solis, discovered the front paws had been cut off. Solis believes the lion was hit by a truck after chasing a deer onto 101.
Mountain lions are a "specially protected species" in California. Hunting them is banned and possession of mountain lion parts or carcasses is also illegal.
"One theory that we're exploring is that someone was listening to a police scanner and was able to get to the scene before our warden," Fish and Game spokesman Andrew Hughan said.