The river flows initially southwards for 1 km (0.6 mi) to a small lake at Baldhorns Park, before running eastwards through a largely rural area towards Crawley. The first tributaries to join the young river drain the northernmost part of St Leonard's Forest, between Horsham and Crawley, although much of the forest is in the catchment area of the River Arun. From Sidlow the Mole turns north west towards Brockham. A number of minor tributaries join the river from the west and are typically second order streams draining the woodland and arable land between Horsham and Dorking. At Leatherhead, the Mole leaves the chalk and turns northwestwards to flow across impermeable London Clay, winding towards Cobham. The water table rises at this point and much of the water which drained out of the channel through the chalk returns through springs in the riverbed. The course of the Mole within the airport perimeter has been altered several times since commercial flights began in 1945; however the meanders visible on the 1839 tithe map in the 1.5 km stretch immediately north of the runway were reinstated in 1999, in a £1.2 million project to facilitate airport expansion.
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