The main rock strata in the Park is composed of igneous and sedimentary rocks.
Igneous rocks are primarily composed of andesite formed during the volcanic activities of the Pleistocene era. Its modes of occurrence include lava flow, agglomerate and tuff, with some basaltic magma and lahar sediments (volcanic mudflow). Andesite is a rock of intermediate composition, and usually contains minerals like hornblende, pyroxene, plagioclase and olivine. Andesite is further classified based on its mineral assemblage, such as the hornblende-pyroxene andesite, Two-pyroxene andesite and olivine-pyroxene andesite. Basalt is a mafic igneous rock, containing minerals like pyroxene, plagioclase and low quantities of olivine.
Sedimentary rock was formed from sediments in a shallow sea environment on the edge of Asian continent, during the late Oligocene to Pliocene Era. The main sedimentary strata include the Wuchishan formation, Mushan formation, Talio formation, Shihti formation, Nanchung formation and Kueichoulin formation. Igneous rocks are deposited on top of sedimentary rocks in an unconventional fashion (discontinuous time intervals).
Andesite rocks that have turned red due to oxidation in the Macao Creek (photo by De Xiong Huang)