The Florida Railroad was the Sunshine State's first cross-peninsular rail line that linked the Atlantic Ocean to the Gulf of Mexico. Construction began in Fernandina in 1855 and was completed to Cedar Key in March of 1861. Over half of the original 155-mile long line is still active as CSX's main line to central and south Florida. However, a 15-mile section between Yulee (milepost 12) and Callahan (milepost 27), in Nassau County, was retired in 1954 when more and more SAL rail traffic was diverted onto the Gross Cutoff.
Most of this abandoned rail bed fell into private hands and is now lost to time, but there is some evidence of this historic railroad still to be found.
Thanks to John Hendricks for contributing information about this route.