It protects the Libunao Spring and surrounding forests, as well as the Nagcullooban River watershed.

[1][2] The Libunao watershed is the source of water supply for domestic use and irrigation of the surrounding farms and communities of northern Ilocos Sur province.

[4] It has an average slope of between 18% and 50% steepness with a soil condition consisting of clay loam.

[5] The park is located approximately 15 kilometres (9.3 mi) from the poblacion or town proper of Sinait and Cabugao and some 36 kilometres (22 mi) north of the provincial capital and heritage city of Vigan.

Its lowland forest contains some leguminous tree species such as mango, narra, mahogany, bangkal, acacia, ipil-ipil, duhat, akleng parang, elemi, tibig, hauili, anabiong and molave.