Driving the Last Spike
This online article from the Museum of the City of San Francisco provides background and primary source information on the construction of the transcontinental railroad.
http://www.sfmuseum.org/hist1/rail.html

California State Railroad Museum
Discover the story of America's first transcontinental railroad and the people who built it. This site contains descriptions, photographs, and paintings that highlight the significance of railroads to the growth of America and convey the drama of linking the Central Pacific and Union Pacific railroads at Promontory Point. Click Rail History to begin.
http://www.csrmf.org/