Although the smallest of Portugal's natural parks, it extends through 72.2 square kilometres (27.9 sq mi) of mountainous land, populated by approximately 700 locals.

Much like a great part of the Transmontana region, PNAL is situated within the Maciço Antigo (Ancient Massif), within the Galiza-Trás-os-Montes subregion, a geomorphological unit of igneous and metamorphic rock formed by Hercynotype movements orienting the first groups along a northeast to southwest axis.

[6] Accompanying these movements were great expansions of granitic magma and prolonged secondary erosion, resulting in sedimentary cliffs and unaccented mountain ranges.

[9] The headlands of the Olo River are influenced by maritime air masses that rise over park's eastern boundary.

[10] Oak trees dominate the major elevated areas, especially along the banks of the river, along with species of Common hazel (Corylus avellana), holly (Ilex aquifolium), chestnut, and laurel, forming mixed forests that include rare plants such as Sundew (Drosera rotundifolia), a species of carnivorous plant found in the moist lands along the riverfront.