The Krol group of rocks, comprising slates, marls, sandstones, limestones and dolomites with a few small dykes intrusives, is the dominant geological formation of Nainital's surroundings, although, Nodules, laminae and stringers of phosphatic material, followed upward by the purple green shales intercalated with muddy finegrained sandstone and siltstone; recognised as the Tal Formation; are also prevalent. The region has a complex geological framework; the rocks are fragile and newly formed. The city is completely located in the catchment area of the Nainital lake, which has highly folded and faulted rocks due to poly phase deformation.