Gorges du Guiers Mort, Deep canyon in Isère, France.

The Gorges du Guiers Mort is a deep canyon in Isère where a river cuts through limestone cliffs, creating a narrow passage with steep walls on both sides. This gorge extends between Saint-Pierre-de-Chartreuse and Saint-Laurent-du-Pont and features towering rock faces that rise sharply from the riverbed.

The site of Fourvoirie marks the entrance to the gorges proper, where the road once had a gate barring access. The former Chartreuse distillery there was abandoned in 1935 after a landslide and has been listed as a monument historique since 1993; the old Fourvoirie forges and the terminus of the Voiron to Saint-Béron railway line also stood on the site. Between Saint-Laurent-du-Pont and Saint-Pierre-de-Chartreuse, 19 bridges were built over the Guiers Mort, several of them classified as monuments historiques.

Nineteen bridges cross the Guiers Mort between Saint-Laurent-du-Pont and Saint-Pierre-de-Chartreuse, several listed as monuments historiques. The Pont de la Tannerie, below the Côte du Moulin, carries the date 1659 on its keystone. The Pont de la Petite Vache, built in the 16th century and classed in 1923, has lost most of its structure to floods, leaving only a few foundation stones.

The gorge is accessible through marked hiking trails starting from the Saint Bruno Bridge parking area, with routes suitable for different fitness levels. Water levels and weather conditions can affect trail difficulty, so wearing sturdy footwear is important for safe footing.

The name Guiers Mort does not mean the river dries up: it distinguishes this stream from the Guiers Vif, the live Guiers, which flows nearby. The two names mark two different rivers of the Chartreuse massif, not the seasonal state of one.