This area is geologically significant. It is the only place where the relationship between the metamorphics of the Kanmantoo Group and the intrusive Reedy Creek granodiorite can be studied. It is the type location for the Reedy Creek granodiorite.
This area consists of Reedy Creek and Caloote Swamp area. Reedy Creek is a small tributary of the River Murray, entering from the west about eight kilometres south-west of Mannum.
The influence of the River Murray extends for a considerable distance along Reedy Creek, partly due to the impoundment of the Murray. Approximately six kilometres before the creek enters the river, it enters a large area of low-lying land, bordered by limestone cliffs. This area consists of large expanses of shallow water connected to the Murray, as well as three pools that evaporate annually to create habitat for waterfowl and waders.
There is also an area of open mudflats formed by silt from the creek. The Reedy Creek area is a significant geological site. Upstream from the Mannum-Murray Bridge road bordering the Caloote swamplands, the creek has cut its way through the Tertiary and Pleistocene to recent sediments which cap the plains, exposing the underlying Kanmantoo Group metamorphic rocks and their associated intrusives.
Adjacent to the road, spectacular granitic tors stand out on the hillside. Two kilometres west of the road, Reedy Creek drops six metres in a waterfall, at the beginning of a gorge cut through the Reedy Creek granodiorite (otherwise known as Tepko granodiorite). At the waterfall there is a nearly vertical contact between this granodiorite and the Kanmantoo Group metamorphic rocks.
The junction of the two rock types is sharp and well exposed. This has allowed study of the problem of whether this is a true intrusive contact or a faulted one. The Reedy Creek Recreation Reserve encloses most of this scenic and geologically significant section of the creek.