The relation of the travertine deposition outcropping in the Bolu and Yeniçaǧa basins located to the west of the North Anatolian Fault System (NAFS) with the faulting of the zone (NAFZ) of the system in this part is examined. These travertines are dated by U - series. Travertine formations in the Bolu and Yeniçaǧa basins are deposited in different ways and localities: on pressure ridges, in the releasing/restraining bends of the strike - slip faults, and around the intersection of faults. While the travertines of the Üçtepeler and Belemur hill are deposited on the pressure ridges, the travertines deposited in Çiǧdem Hill and Çepni are deposited in the releasing/restraining bends of the faults of the zone, and the travertines in Gölköy are deposited on the foot wall of the intersecting of the normal faults which encircles the west side of the basin. As a result of the dating of the travertines on the study area by U - series method, the age data range between 52,649 ± 8040 a and 96,308 ± 17,674 a, and between 17,962 ± 1671 a and 133,463 ± 76,882 a in the Yeniçaǧa and Basins respectively. Information on fault activity is gained as a result of the dating of the travertines deposited due to the strike-slip deformation on different segments of the NAFZ.