[3] The whole area of the Parzonería General de Guipúzcoa y Álava [es] (a communal pasture not belonging to any municipality) is entirely within the park.

[5] The eastern area around Aizkorri and Aratz is mostly formed by Urgonian limestone, which give rise karstic phenomena such as ridges, sinkholes, torques, and ravines.

Notable formations include the La Lece sinkhole, San Adrián tunnel, the Urbia depression, and the Arantzazu ravine.

Species endemic to the Iberian Peninsula include Genista teretifolia, Narcissus asturiensis, N. vardulensis and Saxifraga losae.

[6] Bronze Age remains have been found at the San Adrián tunnel, a natural pass that links Alava and Gipuzkoa.

[7] To the south of the San Adrián tunnel, the remains of a stone paved road extend for about 2.5 km (1.6 mi).