A Fullerton man and a Mexican national were arrested in Newbury Park after their aircraft loaded with 500 pounds of marijuana made an emergency landing, authorities said. Local and federal investigators seized the marijuana, valued at $750,000, and two grams of heroin valued at $700, according to Sgt. Craig Husband of the Ventura County Sheriff's Department. Christopher Shelby, 34, of Fullerton and Mario Fernandez, 38, of Sonora, Mexico, are being held without bail pending arraignment on federal drug charges. The two were flying over Newbury Park when the single-engine Cessna developed engine trouble and made an emergency landing in an open field on Potrero Road.