The only mountain chain proper runs through the south-eastern and eastern part of the Allgäu Alps and forms the Austro-German border. This main chain, with a brief interruption in the area of Rauheck, is built from a very widespread rock formation, known as main dolomite. It begins at the saddle of the Schrofen Pass at the head of the Rappenalpen valley and runs largely in a straight course to the Oberjoch saddle.