A California man was arrested during a traffic stop Sunday after police discovered a "fully loaded AR-15" rifle and a clown mask from the horror movie "It" in the back seat of his vehicle, authorities said.

The vehicle was pulled over on 150th Avenue shortly after 12 p.m. for traffic violations, the San Leandro Police Department said.

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Officers executed a probable cause search of the vehicle and found an AR-15 with a 50-round drum magazine and a bullet in the chamber, according to police. An "It" clown mask and an unspecified amount of marijuana were also found in the vehicle.

A loaded AR-15 style rifle, a clown mask and marijuana were found inside the vehicle, police said.

A loaded AR-15 style rifle, a clown mask and marijuana were found inside the vehicle, police said. (San Leandro Police Department)

The suspect was booked into jail on multiple drug and weapons violations.

Police did not specify why officers initially pulled the man over or immediately release his identity.

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"This was a great traffic stop that took an illegal and dangerous weapon off the street," the department said in a statement. "This is another positive outcome in keeping the citizens of San Leandro safe."