Rikuu West Line

The line was built from the Shinjō end in stages during the 1910s. The first section, from Shinjō to Furukuchi (17.0 km), opened on 7 December 1913 as the Sakata Line (酒田線). It was extended from Furukuchi to Kiyokawa (14.1 km) on 14 June 1914, from Kiyokawa to Karikawa (3.8 km) on 16 August 1914, and finally from Karikawa to Amarume (8.1 km) on 20 September 1914, completing the route down the Mogami valley to the edge of the Shōnai Plain.

The line's identity was reshaped in step with the railways around it. On 1 November 1917, after the completion of the through route on the eastern side of the mountains, the Sakata Line — by then running Shinjō–Sakata together with a Sakata–Mogamigawa freight branch — was renamed the Rikuu West Line, the western half of a Rikuu Line pairing with the Rikuu East Line east of Shinjō. On 20 April 1924, when the Ugo-Kameda–Ugo-Iwaya section opened and linked up with the Uetsu North Line along the Japan Sea coast, the network was reorganised: the Rikuu West Line was redefined as the Shinjō–Amarume section it occupies today, while the Akita–Nezugaseki stretch was folded into the Uetsu Line.

Through the mid-twentieth century the line was modernised in the manner typical of rural JNR routes. On 1 April 1958 all passenger trains were replaced with diesel railcars, ending steam haulage. With the privatisation of Japanese National Railways on 1 April 1987, the East Japan Railway Company inherited the line and freight operations over its whole length were discontinued. Centralised traffic control (CTC) was commissioned on 28 February 1991, removing the need for staffed signalling along the route.

The line was rebranded around the Mogami River and the literary heritage of the valley. On 4 December 1999 the publicly chosen nickname "Oku-no-Hosomichi Mogamigawa Line" came into use, tying the railway to Matsuo Bashō's seventeenth-century journey Oku no Hosomichi, part of which followed the Mogami. KiHa 110 series diesel railcars work the local services that run the length of the line and continue beyond Amarume onto the Uetsu Main Line toward Sakata, the historic destination from which the route first took its name.

The most disruptive event in the line's recent history was not a disaster but a construction project. From 14 May 2022 the entire line suspended train operations and switched to substitute bus service, to allow construction work connected with the (provisional) Takaya Tunnel — part of the Takaya Road, a component of the "Shinjō–Sakata Road" regional high-standard highway being built roughly parallel to the railway. The suspension was originally expected to last only a few years, but it extended well beyond that as the tunnelling progressed.

On 26 September 2025 the Ministry of Land, Infrastructure, Transport and Tourism issued an outlook on the progress of the Takaya Tunnel work and the prospective timing for resuming Rikuu West Line operations and ending the substitute buses. Rail service resumed across the whole line on 16 January 2026; on reopening, however, the very lightly used Uzen-Zennami and Takaya stations were made all-pass, with every train running through without stopping. Today the Rikuu West Line again carries KiHa 110 local services along the Mogami River, a scenic, non-electrified branch whose history spans private-era staged construction, the 1917 Rikuu pairing, the 1924 Uetsu reorganisation, nationalisation, the 1987 transition to JR East, and the 2022 road-tunnel bus substitution.

• 19137 December: the Shinjō–Furukuchi section (17.0 km) opens as the Sakata Line.
• 191414 June: the line is extended from Furukuchi to Kiyokawa (14.1 km).
• 191416 August: the Kiyokawa–Karikawa section (3.8 km) opens.
• 191420 September: the Karikawa–Amarume section (8.1 km) opens, completing the line down the Mogami valley to Amarume.
• 19171 November: the Sakata Line (then Shinjō–Sakata plus the Sakata–Mogamigawa freight branch) is renamed the Rikuu West Line, the western half of the Rikuu Line pairing with the Rikuu East Line.
• 192420 April: the Ugo-Kameda–Ugo-Iwaya section opens and connects with the Uetsu North Line; the network is reorganised, redefining the Rikuu West Line as the Shinjō–Amarume section and folding the Akita–Nezugaseki stretch into the Uetsu Line.
• 19581 April: all passenger trains are replaced with diesel railcars, ending steam haulage.
• 19871 April: with the privatisation of Japanese National Railways, JR East inherits the line and freight operations over the whole line are discontinued.
• 199128 February: centralised traffic control (CTC) is commissioned over the line.
• 19994 December: the publicly chosen nickname 'Oku-no-Hosomichi Mogamigawa Line' comes into use.
• 202214 May: the whole line suspends train operations and switches to substitute buses for construction work connected with the (provisional) Takaya Tunnel on the Takaya Road, part of the 'Shinjō–Sakata Road' regional high-standard highway running roughly parallel to the railway.
• 202526 September: the Ministry of Land, Infrastructure, Transport and Tourism issues an outlook on the Takaya Tunnel work and the prospective timing for resuming Rikuu West Line service and ending the substitute buses.
• 202616 January: rail service resumes across the whole line; on reopening, the very lightly used Uzen-Zennami and Takaya stations are made all-pass, with every train running through without stopping.