Sierra de Algairén is a mountain range in Aragon, Spain, located between the comarcas of Campo de Cariñena and Comunidad de Calatayud. The ridge's highest summit is Pico de Valdemadera (1,276 m).

The Algairén Mountains are covered with forest made up pine, Carrasca (Quercus ilex), cork oak, and also maple trees. They are a Special Protection Area for birds.

These mountains are part of the central area of the Iberian System and the summits are often covered with snow in the winter.

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