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The Atlantic & Pacific completed a bridge across Colorado River on August 3, 1883 and connected with the Southern Pacific line from Mojave. The A&P assumed control of SP line between Needles and Mojave on October 1, 1884. The first bridge was washed away and another bridge was built in 1890 near the current site of Topock. The name of the siding on the Arizona side was renamed from Mellon to Topock in 1904. In 1944, the Santa Fe replaced the old 1890 Red Rock gauntlet bridge with a new double track bridge over the Colorado River. US 66 then used the old railroad bridge until the Interstate 40 bridges replaced it in 1966.
Train 876 (Extra 4649 East) is crossing the double track bridge and moving from California into Arizona on November 2, 1977. Topock is at milepost 565 at an elevation of 550 feet. Disk 73