title: Castlereagh River
context: The Castlereagh rises 20km west of Coonabarabran in the heart of the Warrumbungle mountains[1] at an elevation of about 850 metres.[4] From its commencement upstream in the mountains the river initially flows east through the town of Coonabarabran. It then arcs round south and southwesterly to the village of Ulamambri, then south to Binnaway, and SSW to the small town of Mendooran which lies at the eastern side of the river's hook-shape. From here the Castlereagh flows in a westerly direction at the flattened bottom of the hook and then turns north-westerly towards the town of Gilgandra. From Gilgandra it continues to run northwesterly across the plains through Gulargambone and Coonamble, then continuing across expansive plains, with no urban centres, where elevations are less than 200m, until it joins  the Macquarie River at its uppermost reaches beyond the Macquarie Marshes. Its confluence  with the Macquarie is about 65km SW of Walgett.[2] Not far from the Castlereagh/Macquarie confluence the Macquarie itself joins the Barwon River at a place about halfway between Walgett and Brewarrina.[5][4]
question: Where does Castlereagh River begin?
answers: rises 20km west of Coonabarabran in the heart of the Warrumbungle mountains