Complex sentence: The mountains north of the valley are part of the Central Range, there are four main volcanoes north of the valley, namely, Poás, Barva, Irazú and Turrialba.
Split into simpler sentences: The mountains north of the valley are part of the Central Range. There are four main volcanoes north of the valley, namely Poás, Barva, Irazú and Turrialba.