Several geothermal fields are located in a NE-SW trend along a structural lineament around the Sivas basin; one of those is the Ortakoy travertines situated 83km south-west of Sivas. There are eight fissure-ridge-type travertine localities in the area, although eroded-sheet-type travertines constitute many of the travertines of the region. By evaluating the rocks of the Late Miocene-Early Pliocene Kzlrmak Formation, it was determined that fissure axes developed within fissure-ridge-type travertines, and that the structural elements obtained from satellite images together with the fissures that form the fissure-ridge-type travertines are shear and tension fissures, and the NE-SW-oriented opening of the fissures, were a result of NW-SE-directed compression, which was also responsible for the formation of the Sivas Backthrust. Ground-penetrating radar studies have shown that the thickness of fissure fills within the fissure-ridge-type travertines of the Ortakoy geothermal field increase with depth, and that the hydrothermal fluids which brought about the formation of the travertines moved surfaceward via fissure systems. The results of U/Th radiometric dating indicate that the youngest travertine in the region is 17,761 ((-268)/(+269)) years old and the oldest 128,286 ((-3537)/(+3662)) years old. Using the widths of banded travertines within the fissure-ridge-type travertines as well as these age results, the opening rate of the Sivas Basin was determined to be .06 ((-.01)/(+.05)) mm/year.