Water has always been one of the most important natural resources in arid Colorado and has been the cause of much litigation between individuals, states and water districts. Most of the rivers in Colorado flow west from the Continental Divide making water more scarce on the Eastern Slope. Water diversion projects have carried water from the Western Slope to the thirsty communities and farmlands along the Front Range in Colorado. The Moffat Tunnel was originally built as a tunnel for the Denver & Salt Lake Railroad. However, it was dug as two tunnels with a smaller tunnel, the "pioneer tunnel" used to check construction conditions for a larger bore and for haulage and ventilation during construction. While the railroad tunnel was opened in 1928 the water tunnel began operations in 1936. Now it is lined with concrete, and is an important water conveyor from the Fraser River on the Western Slope to the metro area. The photograph below shows construction of the water portal as of October 22, 1923.