In geographical terms, the Fiordland region contains the huge mountainous regions west of the line from Te Waewae Bay to Monowai to Te Anau, and includes the valleys of the Eglinton River and Hollyford River / Whakatipu Kā Tuka. The area is almost identical to that of the Fiordland National Park, and is marked by U-shaped valleys and fiords along the coast and steep mountains with foundations of hard rocks like gneiss, schist, granite and diorite, with the softer rock having been carved out by multiple glaciations. Fiordland contains New Zealand's oldest known plutonic (igneous) rocks and is dominated by the southernmost extent of the Southern Alps as the peaks reduce in height from north to south.