Most of Gyeongju lies in the Gyeongsang Basin, but a few areas of the city belong to the Pohang Basin, such as Eoil-ri and Beomgok-ri in Yangbuk-myeon, and part of Cheonbuk-myeon. The Gyeongsang Basin areas consist of Bulguksa intrusive rock penetrating layers of sedimentary rocks, mainly granite and porphyry. By contrast, the Pohang Basin areas are made up of stratum that formed in the Tertiary period of the Cenozoic era, which consist of igneous rock, aqueous rock, porphyry, sandstone, and tuff.