The canton is almost entirely mountainous and it is the most sparsely populated region of the country. In its southeastern part lies the only official Swiss National Park. In its northern part the mountains were formed as part of the thrust fault that was in 2008 declared a geologic UNESCO World Heritage Site, under the name Swiss Tectonic Arena Sardona. Another Biosphere Reserve is the Biosfera Val Müstair adjacent to the Swiss National Park, while Ela Nature Park is one of the regionally supported parks. The Grisons shares border with four other cantons: Uri, Glarus, St. Gallen to the northwest (essentially across the Glarus Alps) and Ticino to the west (essentially across the Gotthard Massif and the Lepontine Alps). The Grisons is also the only canton sharing borders with Ticino at the level of the plain, near Roveredo. The canton shares international borders as well with three countries: Liechtenstein to the north, the Austrian regions of Vorarlberg and Tyrol to the northeast and the Italian regions of Trentino-South Tyrol and Lombardy to the south.