The Furka Base Tunnel is a Swiss railway base tunnel on the Matterhorn Gotthard Bahn's Furka–Oberalp line, a west-east railway connecting the cantons of Valais and Uri.
 Its west portal lies east of Oberwald (VS), at 1390 m above sea level and its east portal lies south of Realp (UR), at 1550 m .
 The base tunnel is 15407 m in length, and replaced the previous track that climbed to an apex of 2160 m above sea level, thus allowing year-round service through service on the Furka–Oberalp line.
 The old line has been reopened by the Furka Heritage Railway for tourist trains which pass the Furka Pass via the 1.8 km long Furka Summit Tunnel.
Furka railway station is a metre gauge railway station at the eastern portal of the Furka Summit Tunnel, in the Canton of Uri, Switzerland.
 The station was opened in 1926.
 It was then owned and operated from that point until 1981 by the Furka Oberalp Bahn (FO), which connects Brig in Valais, via Andermatt in Uri, with Göschenen, Uri, and Disentis/Mustér, Graubünden.
The Furka Oberalp Bahn Deh 4/4 I, now known as the Matterhorn Gotthard Bahn Deh 4/4 51–55, is a five member class of metre gauge, rack rail, electric multiple units operated until 2002 by the Furka Oberalp Bahn (FO), and since then by its successor, the Matterhorn Gotthard Bahn (MGB), in the Canton of Valais, Switzerland.
The Brig-Visp-Zermatt-Bahn Deh 4/4, now known as the Matterhorn Gotthard Bahn Deh 4/4 21–24, is a four member class of metre gauge, rack rail, electric multiple unit power cars operated until 2002 by the Brig-Visp-Zermatt-Bahn (BVZ), and since then by its successor, the Matterhorn Gotthard Bahn (MGB), in the Canton of Valais, Switzerland.
Furka Pass,(French: "le col de la Furka" ), with an elevation of 2429 m , is a high mountain pass in the Swiss Alps connecting Gletsch, Valais with Realp, Uri.
 The Furka Oberalp Bahn line through the Furka Tunnel bypasses the pass.
 The base tunnel opened in 1982 and replaced a tunnel at 2100 m.
The Furka Cogwheel Steam Railway (Dampfbahn Furka-Bergstrecke, DFB in German) is a largely volunteer operated heritage railway which operates a partially rack and pinion-operated line across the Furka Pass, between Realp in Uri and Oberwald in Valais.
 Culminating at 2160 m , above sea level, it is an old mountainous section of the Furka Oberalp Bahn (FO) that was abandoned after the construction of the Furka Tunnel.
 It has been gradually brought back into service by the Verein Furka-Bergstrecke with the use of only steam locomotives, with the entire line completed in 2010.
 The Furka Railway is the second highest rail crossing in Europe, after the Bernina Railway.
 The Uri side of the line also constitutes the highest railway in Central Switzerland.
The canton of Valais (] ; German: "Wallis" , ] ) is one of the 26 cantons of Switzerland, situated in the southwestern part of the country, around the valley of the Rhône from its headwaters to Lake Geneva, separating the Pennine Alps from the Bernese Alps.
 The canton is simultaneously one of the driest regions of Switzerland in its central Rhône valley and among the wettest, having large amounts of snow and rain up on the highest peaks found in Switzerland.
 The canton of Valais is widely known for the Matterhorn and resort towns such as Crans-Montana, Saas Fee and Zermatt.
 It is composed of 13 districts (hence the 13 stars on the flag) and its capital is Sion.
The Furka Oberalp Bahn Deh 4/4 II, now known as the Matterhorn Gotthard Bahn Deh 4/4 91–96, is a class of metre gauge, rack rail, electric multiple unit power cars operated until 2002 by the Furka Oberalp Bahn (FO), and since then by its successor, the Matterhorn Gotthard Bahn (MGB), in the Canton of Valais, Switzerland.
Deh Sir (Persian: ده‌سیر‎ ‎ , also Romanized as Deh Sīr; also known as Deh-e Shīr and Deh Zīr) is a village in Qilab Rural District, Alvar-e Garmsiri District, Andimeshk County, Khuzestan Province, Iran.
 At the 2006 census, its population was 23, in 4 families.
The Rhône Glacier (German: "Rhonegletscher" , Walliser German: "Rottengletscher", French: "le glacier du Rhône" ) is a glacier in the Swiss Alps and the source of the river Rhône and one of the primary contributors to Lake Geneva in the far eastern end of the Swiss canton of Valais.
 Because the Glacier is located close to the Furka Pass road it is easily accessible.

Question: Furka–Oberalp-Bahn Deh 4/4 I was operated in which southwestern Swiss canton?
Answer: Valais