Mountain & Origin

Piz Sardona: the mountain behind the water

Piz Sardona, Surenstock in German, is a 3,056-metre summit on the border between the cantons of St. Gallen, Glarus and Graubünden. It lends its name to a UNESCO World Heritage Site, to an entire mountain region and to a mineral water. Researchers have been travelling here for more than a hundred years, drawn by rock faces in which the making of the Alps can literally be read; and high on its flanks begins the journey that turns snow and rain into a naturally alkaline mineral water.

Updated August 2026 · 6 min read

Where is Piz Sardona?

Piz Sardona stands where the cantons of St. Gallen, Glarus and Graubünden meet, in high-alpine border country between the Sarganserland, the Sernftal in Glarus and the Vorderrhein valley in Graubünden. At 3,056 m above sea level, it ranks among the highest peaks of the region; its neighbours include the Ringelspitz and the Trinserhorn. The mountain's German name is Surenstock, yet the Romansh name “Piz Sardona” has prevailed, on many maps as well.

The surroundings are comparatively secluded: on the St. Gallen side, the Weisstannental and the Calfeisental lead towards the massif; on the Glarus side, the Sernftal with the village of Elm; on the Graubünden side, the area around Flims and Trin. Smaller glaciers such as the Sardona glacier shape the north side of the massif; as almost everywhere in the Alps, they have shrunk markedly in recent decades.

What makes the Tectonic Arena Sardona a UNESCO World Heritage Site?

The Swiss Tectonic Arena Sardona has been a UNESCO World Heritage Site since 2008 – one of the few sites worldwide inscribed solely for their geology. The area covers around 300 square kilometres of mountain landscape around Piz Sardona, the peak that gives it its name. At its centre lies the Glarus thrust: a strikingly sharp line in the rock faces along which older rock layers were pushed over considerably younger ones.

Normally, younger rocks lie above older ones; in the Tectonic Arena it is the other way round. As the Alps folded, entire packages of rock were thrust over one another across many kilometres, and hardly anywhere else is this process of mountain building so clearly visible over such a distance. The phenomenon occupied European geology as early as the 19th century and contributed substantially to the understanding of how mountains form. Best known is the view from Elm of the Tschingelhörner with the Martinsloch, a natural rock window in the immediate vicinity of the thrust line.

Can you climb Piz Sardona?

Yes, though Piz Sardona is a high-alpine objective for experienced mountaineers. Depending on the route, the ascent leads over firn and boulder terrain; a frequent starting point is the SAC Sardona hut at the far end of the Calfeisental. Those who would rather experience the World Heritage Site without summit ambitions will find marked hiking trails and viewpoints in the region with clear views of the Glarus thrust, including on multi-day routes through the World Heritage area.

Specific route descriptions, difficulty grades and current conditions are matters we deliberately leave to the touring portals and to the hut teams and mountain guides on the ground, where this information is maintained with expertise and kept up to date. High-alpine tours require experience and careful planning, plus equipment to match.

What does Piz Sardona have to do with mineral water?

The connection lies quite literally in the mountain. At over 2,000 m above sea level, in the Sardona Alps by the UNESCO World Heritage Site, lies the infiltration area of the Castelsquelle spring: meltwater and precipitation seep into the ground there and begin a journey through the rock that takes years.

On the way down, the mountain acts as a natural filter. Layer by layer, the rock holds back particles while the water gradually dissolves minerals: calcium and hydrogen carbonate from limestone, for example, or sulphate from sulphate-bearing strata. The mineralisation a water finally shows is thus a direct image of the geology it has passed through. How mineral water differs legally from spring water is explained in our article Spring water or mineral water.

How does this become the water of the Castelsquelle?

The water travels through layers of rock and stone for around 12 years before it is drawn from the Castelsquelle in Mels, in the Sarganserland. What emerges is a naturally alkaline mineral water with a pH of 8.0, and the long passage through the mountain explains its composition. Per litre, it contains:

• Calcium: 87 mg
• Magnesium: 35 mg
• Sulphate: 265 mg
• Hydrogen carbonate: 133 mg
• Sodium: 4 mg
• Total mineralisation: 540 mg

Striking are the low sodium content of 4 mg per litre and the comparatively high sulphate value of 265 mg, both traces of the rock strata the water has flowed through. With a total mineralisation of 540 mg per litre, it is moderately mineralised overall. The depth and duration of the passage also shield the water from surface influences. In Switzerland, natural mineral water must be bottled directly at the source. Read more about its character and values under our water.

The mountain is thus a geological textbook case and, at the same time, the origin of a water whose character forms inside it. We retrace the whole journey, from the infiltration area at over 2,000 m above sea level to the spring catchment in Mels, on our Origin page.

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