The river has two main tributaries, the first of which begins several hundred metres south of Hensbarrow Beacon at grid reference and heads south east past the southern edge of Gunheath china clay pit. At Carthew, the river heads south and passes Ruddlemoor and Trethowel in the Trenance Valley, where several mills and blowing houses made use of the river. This is a steep sided ‘V' shaped valley carved through granite. A number of very minor tributaries enter this section, including springs and adits/levels at Gunheath, Lansalson, and Bojea. At the end of the Trenance Valley the river passes under the Cornish Main Line railway and enters St Austell.