Legally the Eaux Vives line is neither French nor 'Swiss'. The Swiss section is the Chemin de fer de l'Etat de Genève (Geneva State Railway).
Here's an extract from an article an article of mine that has been published in the SNCF Society Journal:
the Annemasse Genève Eaux Vives line, which is set to be the line most affected by the CEVA project. This line was the only part of the original planned loop from Haute Savoie into Genève Cornavin to be built, and was opened in 1888. Just 6km long it crosses the border 2km after leaving Annemasse, then runs for 4km through back yards of the expanded Geneva suburbs, through the station at Chêne Bourg serving what was once a separate town but is now a suburb of Geneve.
Although at face value an SNCF line, the 4km section in Switzerland belongs to the Canton (State) of Geneva and is therefore arguably one of the smallest state railways in the world! Its legal title is Chemin de fer de lEtat de Geneve (Geneva state railway).
The line parallels Geneva tram route 12, which itself ran beyond the border (and present terminus) at Moillesulaz into Annemasse until 1958. Chêne Bourg station was closed in the mid 1980s and replaced by a station in the French suburb of Ambilly which is squeezed in between Annemasse and the Swiss border. The line was 100% steam worked until the arrival of SNCF diesel railbuses and railcars in the 1950s, and subsequently electrified in 1986. Despite the regular shuttles being railcar, some peak period steam services ran through to the mid-1960s. For such a short line, it has seen a remarkable number of different classes of diesel and electric railcars used since the 1950s, culminating in the use of some of the latest French TER Rhône Alpes double deck EMUs. The associated branch from Annemasse to La Roche sur Foron does not immediately affect Switzerland but does carry passengers from Geneva travelling to Annecy or St Gervais, particularly at summer weekends and for skiing in winter.
Gordon
Technical Adviser SNCF Society
Family resident near Geneva since 1949