The Nature Reserve lies at the south-eastern edge of Prealpi Carniche, with the large bed of River Tagliamento separating them from Prealpi Giulie, the hills, and the upper Friulana plain. It covers most of Tagliamento riverbed between the town of Peonis and the bridge near Cornino, for a total length of almost six kilometers. It includes meadows and cultivated fields adjacent the towns and extending towards the west, involving the large rocky amphitheater above Somp Cornino, the lake, and the steep walls and detrital cones that, in the north, separate Tagliamento from the mountains. Despite reaching not very high altitudes, the difference in height is considerable and goes from the 170m asl of the river to the 700m of the plateau of Mt. Prat.