The rock formations in the Ötz valley belong to the geological system called the Ötz valley-Stubai Complex. The main formations are composed of acidic Ötz valley gneiss (mica schist and paragneiss) with insertions of orthogneiss and amphibolite. South of Obergurgl, for example at the the end of the Gaisberg and Rotmoos valleys, one can find limestone of the “Schneeberger Zug.” The stone succession consists of yellow and grey marble, mineral rich mica shist and amphibolite. The mica, with its inlaid garnet and hornblende crystals, is noticable because the crystals can be up to several cm large.
A well-known area to find garnets is the “Granatkogel” (Garnet mountain) on the east side of the Gaisberg valley. In summer, around the tongue of the Gaisberg glacier, one can find beautiful garnet crystals which derive from the Granatkogel as a result of rockslides and avalanches and from melting ice. Since the ice age, rock slides have continuely shaped the landscape of the Ötz valley. The Winkelberg intertreptive geological trail and the Forchet interpretive nature trail offer fascinating insights into the geological past of the Ötz valley.