Covering 1,800 hectares of the Darling Range, tucked behind the Darling Scarp, covering both sides of a steep valley; the Avon River joins the Brockman River to form the Swan River which passes through the tree lined valley.
The area is dominated by granite outcrops along with smaller dolerite areas, the tops of the hills are topped with laterite.
Walyunga contains one of the largest known Aboriginal campsites around Perth and was still in use by the Nyoongar people late last century. The area has been used as a meeting place for more than 6,000 years. Walyunga ia an Aboriginal name, but its meaning is uncertain. It could be a term that, roughly translated, means 'happy place'. Local Nyoongar people believe the Swan River was carved by the Wuagal, and greet the dreamtime serpent here by rubbing sand on their bodies and throwing it in the water.
The Swan River is the main attraction in the park as it thunder through in winter and meanders by in the drier months, lined with smooth granite boulders. This section of the Swan is characterised by rapids followed by deep pools, and in the park these can be experienced at Syd's Rapids. Walyunga Pool and Boongarup Pool.
The valley floor is home to flooded gums at the river's edge, while fuirther up the slopes are wandoo woodlands giving way to marri and powderbark on the rises and jarrah on the ridges. The woodland understorey is lovely in the spring when it comes alive with wildflowers.
There are many walk trails through the park.
After high amounts of rain the Swan River can flow rapidly through the park and care must always be taken around rapids and slippery rocks. Commuter and goods trains also frequently pass through the park.