A 20 car derailment early Monday morning shut down two lines of the Union Pacific Railway. A Union Pacific spokesman says the derailment happened at about 1:45 a.m. just east of Cheyenne as the train was headed toward North Platte. No injuries were reported and all the cars were empty at the time. One of of the tracks was reopened this morning and crews worked on gettting the other track opened throughout the day. Still no word on what caused that derailment.