The river valley is the centre of the catchment of the
Helena River and extends from the edge of the Darling Scarp where
Boya,
Gooseberry Hill and Helena Valley define the "mouth" of the valley that opens to the
Swan Coastal Plain, east and south east past
Mundaring Weir and
Lake C.Y. O'Connor to its origins in the region of
Mount Dale. The soils of Helena Valley are characteristic of the eastern
Swan Coastal Plain, ranging from sand to
loam and
clay, with a neutral
pH tending towards moderately acid. ==Locality==