The reservoir of Monte Sant 'Onofrio and of the chain Monte Cane, from which descends the water "Milicia", is located in the natural reserve of "Pizzo Cane, Pizzo Trigna and Cave Mazzamuto".
The reserve, extended 4641.43 Hectares, is considered one of the most interesting in the province of Palermo for its great geomorphologic and naturalistic variety. In the faunal community there are rare species of prey, martens, the Wild Cat, porcupines and the Hare Apennine. The natural forests are mostly made up of oak, from the cork oak and deciduous oak, together with ash and field maple. In the undergrowth there are bushes of roses typical of the Mediterranean: evergreen rose, common hawthorn, heather, gorse and laburnum. The caves Briglia, Mazzamuto and Leone are particularly important from the point of view of paleontological caving. The cave Briglia spans several rooms connected by tunnels and registers the presence of spectacular stalagmites and stalactites, while in the cave Mazzamuto was found the fossil of a dwarf elephant and various signs of the presence of primitive Epigravettian settlements.