The Theodulgletscher Slice is an Upper Penninic tectonic unit situated between the Zermatt-Saas Fee Nappe and the Tsaté Nappe. It comprises eclogitic continental basement rocks similar to that of the structurally higher Dent Blanche and Sesia nappes. It is likely derived from extensional allochthons, formed during the Jurassic opening of the Piemonte-Liguria Ocean in a more distal position than the Cervinia Terrane from which the Salassic nappes originate.