An average of 120 train cars ran along the line each hour, transporting fill that was mainly excavated from enormous piles of hydraulic mining debris that was washed down by the Feather River after the California Gold Rush. On December 22, 1964, disaster nearly struck when the Feather River, after days of heavy rain, reached a peak flow of above the Oroville Dam site. The water rose behind the partially completed embankment dam and nearly overtopped it, while a maximum of poured from the diversion tunnels. This Christmas flood of 1964 was one of the most disastrous floods on record in Northern California, but the incomplete dam was able to reduce the peak flow of the Feather River by nearly 40%, averting massive damage to the area. Ten months later, four men died in a tragic accident on the construction rail line. On October 7, 1965, two 40-car work trains, one fully loaded and the other empty, collided head-on at a tunnel entrance, igniting of diesel fuel, completely destroying two locomotives. The burning fuel from the collision started a forest fire that burned before it could be extinguished. The crash delayed construction of the dam by a week while the train wreckage was cleared. Overall, 34 men died in the construction of the dam. Oroville Dam was designed to withstand the strongest possible earthquake for the region, and was fitted with hundreds of instruments that serve to measure water pressure and settlement of the earth fill used in its construction, earning it the nickname "the dam that talks back". (A ML 5.7 earthquake in the Oroville area in 1975 is believed to have been caused by induced seismicity from the weight of the Oroville Dam and reservoir on a local fault line.) The embankment was finally topped out on October 6, 1967, with the last of 155 million tons (140.6 million t) of material that took over 40,000 train trips to transport. On May 4, 1968, Oroville Dam was officially dedicated by the state of California. Among the notable figures present were California governor Ronald Reagan, who spoke, Chief Justice (formerly California governor) Earl Warren, Senator Thomas Kuchel, and California Representative Harold T. "Bizz" Johnson. The dedication was accompanied by a week of festivities in nearby Oroville, attended by nearly 50,000 people. 2005 dam relicensing On October 17, 2005, three environmental groups filed a motion with the Federal Energy Regulatory