The Saar River rises in the Vosges mountains on the border of Alsace and Lorraine, in France, then flows northward through western Germany to its confluence with Mosel river, near Trier. Within Germany the Saar River pursues a winding course until it reaches a barrier in the form of Hunsrück, a low mountain range made of hard quartzite rock. Quartzite is a hard, metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression. The river, unable to carve a way through the rocks, makes a full 180-degree turn and cuts a deep U-shaped gorge through the thickly wooded mountains. This remarkable hairpin bend located above Mettlach is called the Saar Loop or Saarschleife in German, and is one of the most famous sights of Saarland. The river flows parallel for a long stretch in the opposite direction before turning left and continuing its northward journey towards Mosel river.