Mountain ruoute: San Lázaro (1.268 m.)
San Lazaro and San Mamés, its twin top guarding the gate of Medina on the way from Valdivielso to Urría
organizes: Club Montes Obarenes.
The Sierra of Tesla is a long limestone wall that separates the lands of Medina de Pomar, crossed by the Nela, Valdivielso, watered by the Ebro River. Through the center ran a route of Roman origin then used by the Visigoths (s. VI), beginning in Quintanalacuesta. It is tracing the hard side, and the called gate of Medina, down to Tartalés de los Montes.