The Val di Mello Nature Reserve - established with the Decision of the Lombardy Regional Council n. 802 of the 27th January, 2009 - occupies the right side, where the Masino valley splits near the built-up area of S. MArtino (932 m). The Mello valley is placed in a South-West, North-East direction, with a mild valley bottom ending in the locality of Rasica (1,148 m), the tributary valleys raise up to very high altitudes (the mount Pioda is the highest one with 3,341 m). The Nature Reserve includes the whole hydrographic basin of the stream Mello. The Cavalcorto ridge represents the western border, between the Ferro valley and the Porcellizzo valley.