The Sierra de Tenango or Sierra Norte de Puebla mountain range begins to one side of the Valley of Tulancingo and extends down to the Huasteca region of Puebla and Veracruz states. The range is also known as the Sierra de Huayacocotla, with low lying mountains of a humid, cloudy temperate climate with frequent rain in the summer. Two of Hidalgo's main dams, the Tejocotal and the Omitemetl are located on the rivers here, and are part of the Necaxa Hydroelectrical System.