Yonesaka Line

The railway was envisaged under the old Railway Construction Act as a connecting line between the Hokuetsu and Ōu lines, linking Shibata in Niigata Prefecture with Yonezawa in Yamagata Prefecture, and it was built inward from both ends over a decade. On 28 September 1926 the Yamagata-side section from Yonezawa to Imaizumi (23.0 km) opened as the Yonesaka Line, with new stations at Minami-Yonezawa, Nishi-Yonezawa, Chūgun, Uzen-Komatsu and Inukawa. On 10 August 1931 the line was extended from Imaizumi to Tenoko (11.7 km) and renamed the Yonesaka East Line, while on the same day the Niigata side opened independently as the Yonesaka West Line, from Sakamachi to Echigo-Shimoseki (11.0 km). Both halves then pushed toward each other: the eastern line reached Uzen-Numazawa in 1933 and Oguni in 1935, and the western line reached Echigo-Kanamaru in 1933.

The two lines met on 31 August 1936, when the final Oguni–Echigo-Kanamaru section (9.5 km) opened across the prefectural border, completing the through route from Yonezawa to Sakamachi (90.7 km), reunifying the two halves as the Yonesaka Line and adding Tamagawaguchi Station. For decades the line served as an important passenger and freight link between the Sea-of-Japan coast and the inland Tōhoku, chiefly between Niigata and the Yamagata and Sendai areas. From 1 November 1960 the semi-express Asahi ran between Sendai and Niigata via the Senzan, Ōu, Yonesaka and Uetsu lines; it was upgraded to express status on 5 March 1966. Disasters punctuated this period: on 5 March 1940 an avalanche destroyed an Arakawa river bridge between Oguni and Tamagawaguchi and a Yonezawa-bound-for-Sakamachi train's locomotive plunged some 25 metres into the river, killing 15 people and injuring 30, and in the Uetsu heavy rain of 28–29 August 1967 the line suffered damage at 102 locations, with full restoration only on 28 June 1968.

When Japanese National Railways was divided and privatised on 1 April 1987, JR East took over the line and freight services between Yonezawa and Sakamachi were discontinued. The line's role as a trunk feeder steadily faded with the rise of motorisation, the end of freight, and the electrification of the parallel Uetsu Main Line, which removed much of its value as a diversion route for limited expresses; after the Ōu Main Line was regauged to standard gauge for the Yamagata Shinkansen, through running survived only toward Niigata. The express Asahi had been renamed Benibana on 1 May 1982 ahead of the Jōetsu Shinkansen's opening, and on 27 August 1991 the Benibana was downgraded to a rapid service between Yonezawa and Niigata as the Yamagata Shinkansen works advanced. On 1 December 1995 Tamagawaguchi and Hanatate stations were closed — the first station closures in JR East's network since the company's founding in 1987, setting aside transfers of designated local lines to third-sector operators. On 14 March 2009 the rolling stock was unified on KiHa E120 and KiHa 110 series diesel cars and one-man operation began, and from the March 2020 timetable the GV-E400 series replaced the KiHa E120, leaving KiHa 110 and GV-E400 cars in service.

The Yonesaka Line has repeatedly been disrupted by snow and rain. The whole line was suspended after the Tōhoku earthquake of 11 March 2011, reopening in stages on 14 and 20 March, and floods and landslides forced bus substitution in 2004, 2005, 2013 and 2014. The most serious blow came in the concentrated rainfall of 3–4 August 2022, when the village of Sekikawa along the line recorded hourly rainfall of 150 mm. The entire line was suspended on 3 August; the next morning the small Kosshogawa bridge between Uzen-Tsubaki and Tenoko was confirmed to have collapsed, and a survey found 112 damaged locations between Imaizumi and Sakamachi, with 43 of them concentrated between Uzen-Tsubaki and Uzen-Numazawa. The Yonezawa–Imaizumi section reopened on 9 August 2022, but the Imaizumi–Sakamachi section has remained closed, served by a replacement bus operated by Niigata Kotsu from 12 August 2022.

The long severance has put the line's future in question. On 25 April 2023 JR East's Niigata branch announced that restoration would cost about 8.6 billion yen and take an estimated five years, and said that a sum that large was difficult for the company to shoulder alone, signalling that it wished to discuss cost-sharing with the national government and with Yamagata and Niigata prefectures and the line's municipalities. At a restoration study meeting on 29 May 2024 JR East stated that restoration on the previous JR-operated basis would be difficult and laid out four options for the line's future: continued JR operation, a vertical-separation scheme in which local governments would own the infrastructure while JR ran the trains, operation by a third-sector company, or conversion to bus. As of 2026 the Imaizumi–Sakamachi section remains suspended and bus-substituted while these options, including a trial of bus operation, are under discussion.

• 192628 September: the Yonezawa–Imaizumi section (23.0 km) opens as the Yonesaka Line, with new stations at Minami-Yonezawa, Nishi-Yonezawa, Chūgun, Uzen-Komatsu and Inukawa.
• 193110 August: the line is extended from Imaizumi to Tenoko (11.7 km) and renamed the Yonesaka East Line; the same day the Sakamachi–Echigo-Shimoseki section (11.0 km) opens independently as the Yonesaka West Line.
• 193310 November: the eastern line is extended Tenoko–Uzen-Numazawa (9.2 km); 30 November: the western line is extended Echigo-Shimoseki–Echigo-Kanamaru (11.9 km).
• 193530 October: the eastern line is extended from Uzen-Numazawa to Oguni (14.4 km), with new stations at Isaryō, Uzen-Matsuoka and Oguni.
• 193631 August: the final Oguni–Echigo-Kanamaru section (9.5 km) opens across the prefectural border; the Yonezawa–Sakamachi through route (90.7 km) is completed and the two halves are reunified as the Yonesaka Line; Tamagawaguchi Station is added.
• 19405 March: an avalanche destroys an Arakawa river bridge between Oguni and Tamagawaguchi; the locomotive of a Yonezawa-to-Sakamachi train falls about 25 m into the river, killing 15 people and injuring 30 (Yonesaka Line avalanche-strike accident).
• 19601 November: the semi-express Asahi begins running between Sendai and Niigata via the Senzan, Ōu, Yonesaka and Uetsu lines.
• 196728–29 August: the Uetsu heavy rain damages the line at 102 locations; full restoration is achieved on 28 June 1968.
• 19871 April: with the division and privatisation of Japanese National Railways, JR East takes over the line and freight services between Yonezawa and Sakamachi are discontinued.
• 199127 August: the express Benibana (renamed from Asahi in 1982) is downgraded to a rapid service between Yonezawa and Niigata as the Yamagata Shinkansen works advance.
• 19951 December: Tamagawaguchi and Hanatate stations are closed — the first station closures in JR East's network since its 1987 founding, excluding transfers of designated local lines to third-sector operators.
• 200914 March: rolling stock is unified on KiHa E120 and KiHa 110 series diesel cars and one-man operation begins.
• 201111 March: the whole line is suspended by the Tōhoku earthquake; it reopens in stages, Oguni–Sakamachi on 14 March and Yonezawa–Oguni on 20 March.
• 20223 August: concentrated rainfall (150 mm/h recorded at Sekikawa) suspends the whole line; the Kosshogawa bridge between Uzen-Tsubaki and Tenoko collapses and 112 damage sites are found between Imaizumi and Sakamachi. Yonezawa–Imaizumi reopens on 9 August, but Imaizumi–Sakamachi remains closed, served by a replacement bus (Niigata Kotsu) from 12 August.
• 202325 April: JR East's Niigata branch announces that restoration would cost about 8.6 billion yen over an estimated five years and that the cost is too large to bear alone, seeking cost-sharing with the national government and the prefectures and municipalities.
• 202429 May: at a restoration study meeting, JR East states that restoration on the previous JR-operated basis would be difficult and presents four options: continued JR operation, a vertical-separation scheme, operation by a third-sector company, or conversion to bus.