The Gross Cutoff was built by the Seaboard Air Line around 1925 so their passenger trains could bypass the congested Union Terminal in Jacksonville. Florida was a major tourist destination and they had to upgrade their rail line in order to compete with their rival, the Atlantic Coast Line. Named for a small turpentine village on the SAL line just south of the Georgia State Line (near the present day intersection of I-95 and US 17), the bypass veered off to the southwest, joining the old Florida Railroad on a curve 1/2 mile east of Callahan. Once completed, the 13-mile long bee line sans curves funneled much of their passenger trains through the thick pine forests of Nassau County to Callahan and onto Tampa, St. Petersburg and Miami. After the ACL and SAL merged in 1967, the newly formed Seaboard Coast Line selected the double-tracked ACL line from Savannah as their primary line, regulating the Gross Cutoff to Amtrak passengers trains and local manifests. By 1985, CSX deemed the cutoff unnecessary, abandoning the line entirely from their live tracks in Callahan northeastward to I-95 and US 17.
Today most of the line runs through a privately owned timber management area, although CSX claims ownership of about 2 miles of the bed in Callahan.
Thanks to John Hendricks for contributing information about this route.