The ferruginous sandstone of Puisaye used for the construction of the fortified castle of Guédelon is a yellow-orange to brown rock made up of mainly quartz sand and ferruginous cement. It forms a south-west-north-east oriented deposit between the Yonne and the Loire. This deposit separates the limestone plateaus of the Auxerrois from the chalk lands of the Sénonais. The sandstone intercalations present locally in the sands of Puisaye contain seventeen of the twenty open pit quarries identified in the region. The two main extraction areas are located between Toucy-Parly-Pourrain and Saint-Sauveur-en-Puisaye-Moutiers-Treigny near the Guédelon construction site.