The Vallée de Joux is a valley of the Jura Mountains mainly in the Swiss Canton of Vaud. The valley also continues into France (Département of Jura) at its higher, south-western, end. Located 30 miles (50 km) north of Geneva and north-west of Lausanne, its mean elevation is over 3300 feet (1000 metres). There are three Swiss lakes in the Vallée de Joux : the lac de Joux (around 6 miles (10 km) long), the lac Brenet and the lac Ter. The French border runs along the northern edge of the valley until, about 10 km west of the lac de Joux, the base of the valley becomes French territory.