The Nature Reserve, situated in the south-west of the town of Siena, includes a long stretch of the river Merse, the stream Ricausa, most part of the stream Rosia and the last stretch of the stream La Gonna, all tributaries of the river Merse. Most part of the mountains, in particular those where the siliceous rocks belonging to the Verrucano Group outcrop, is covered by deciduous woodlands where the Turkey oak dominates, since it well adapts to siliceous soils. In the lower part of the slopes, which are cooler, together with the Turkey oak we can also find the Sessile oak. After Sessile oak woods, Chestnut tree woods are the most widespread woodland habitat in the Nature Reserve.