In 1930, the Union Pacific built a branch line from a junction on its Los Angeles & Salt Lake mainline, just south (west) of Las Vegas, to the construction site for Boulder Dam. The branch passed through Henderson to Boulder City at the end of the line.
A separate US Government railroad was built from Boulder City to the actual dam construction site on the Colorado River. The dam was completed in 1935, and the US Government line was abandoned at that time. Much of the right of way of the Government railroad is underneath Lake Mead.
The UP continued to actively use its line as far as Henderson, and still does today. In 1985, the UP donated the Henderson-Boulder City segment to the Nevada State Railroad Museum. This segment is still in place, although the grade crossing near Railroad Pass is paved over (see photo below). Some of the track has been upgraded, and a station platform and engine shed were built. There are plans to start operating tourist trains within a year or two.