The very northern part of the Valley of Mexico is located within the state, which is separated from the area in which Mexico City is found by a series of low lying mountains. This part of the Valley extends from Tizayuca towards Pachuca. It is separated from the Valley of Mezquital by the Sierra de Tezontlalpan and from the rest of the Valley of Mexico by the low lying Sierra de los Pitos. The climate here is temperate and semi arid with occasional freezes. Except for the forests on the mountain tops, the flora and fauna are those found in more arid regions such as maguey, yucca, rabbits, armadillos and mesquite trees.