Ge 4/4 II # 613 of the Rhaetian Railway pulls the PE 905 GLACIER EXPRESS St.Moritz-Zermatt on the section between Chur and Disentis/Mustér, through the gorge of the Vorderrhein, called Ruinaulta, near Versam-Safien. The Ruinaulta gorge was formed after the Flims landslide almost 10,000 years ago. At that time, more than 10 billion cubic meters of rock broke off between the Flimserstein and the Piz Grisch and buried the Vorderrhein valley between the present-day villages of Castrisch and Reichenau under a mass of debris several hundred meters thick.
Since the Vorderrhein could no longer flow away, a lake was dammed over a length of about 25 km. In the course of time, the river cut deeply into the loose landslide masses and the water from the resulting lake was able to flow out again. When erosion cut through the landslide fan down to the valley floor, the Ruinaulta formed a gorge with steep limestone scree cliffs that gradually continued to erode. This created imposing erosion formations on the valley flanks.