The plains at the foot of the Sierra Madre Occidental is an elongated mesa known as Altiplanicie Mexicana that exhibits a steppe climate and serves as a transition zone from the mountain climate in the western part of the state to the desert climate in the eastern side of the state. The steppe zone accounts for a third of the state's area, and it experiences pronounced dry and wet seasons. The pronounced rainy season in the steppe is usually observed in the months of July, August, and September. The steppe also encounters extreme temperatures that often reach over 100 °F in the summer and drop below 32 °F in the winter. The steppe zone is an important agriculture zone due to an extensive development of canals exploiting several rivers that flow down from the mountains. The steppe zone is the most populated area of the state.