The Union Pacific Railroad (UPRR) causeway is a 20-mile railroad bridge that crosses the Great Salt Lake in Utah. It separates the lake into a north arm and a south arm. The causeway is a vital transportation corridor and a key part of Union Pacific's network. The different colors of the arms is from the level of salinity and bacteria that grows in the north arm which has less fresh water inlets. The access of water between the North and the South Arms are cut off sacrificing the north arm to protect the South Arm. March 2nd, 2025. Photo- EcoFlight?Sallie Dean Shatz.