Originally, all the lines were gauge narrow gauge railways, starting with the line from Port Pirie in 1875, extended to Petersburg (now Peterborough) in 1880 and to Cockburn (on the state border near Broken Hill) in 1888. A branch from Gladstone to Laura in 1884 was extended to Wilmington in 1915. The line from the south (extending the line that terminated at Blyth) was completed in 1894. In 1927, the line from Hamley Bridge through Blythe to Gladstone was converted to broad gauge, making Gladstone a break-of-gauge junction.