The Brurastakken area consists of sedimentary rocks from the Silurian period, resting in primary sedimentary contact on older metamorphic sediments of the Høyvik Group. Above these rocks lie the mixed sedimentary rocks of the Sunnfjord mélange, composed of both continental and oceanic material. These formed during the emplacement of ocean-floor rocks from the Iapetus Ocean in connection with the formation of the Caledonides.
The sequence contains exceptionally well-preserved sedimentary rocks representing environments from continental to deep-marine settings, locally with fossils such as corals, crinoids and brachiopods from the Silurian period. These sedimentary layers are folded into a large and particularly spectacular structure, one of the most beautiful and clearly visible folds in Norway.