The first common carrier rail line in California was built between Sacramento and Folsom, in the foothills of the Sierra Nevada Mountains. It was eventually absorbed into the Southern Pacific.
Around the 1980s the eastern end of the line, between Nimbus and Folsom, was abandoned. The right-of-way was used to extend US 50 as a divided highway; the ROW was paved over by the new eastbound lanes. The abandonment in turn forced the closure of the SP branch to Placerville. This Placerville branch diverted from the SP line to Folsom near Natoma.
In the late 1980s, Sacramento began operation of its light rail line; the southern leg was built along the SP Folsom branch. Over the years the light rail line has extended further eastward. In 2004-2005, the extension to Folsom was approved, and the rails returned to Folsom. The eastern end of the light rail line runs parallel to the former right-of-way of the SP, since the light rail line was added after US 50 was widened.
Thanks to Mike Palmer for contributing information about this route.