Latitude -32.833906, Longitude 150.205032
Located in the Sydney Surrounds Region of NSW, nearest town Rylstone
The spectacular pagoda rock formations at Dunns Swamp are Triassic age Narrabeen Sandstone formed by the deposition of water borne sediments, approximately 200 million years ago. The type of sediment deposited is determined by the flow of the water, with gravel, forming conglomerate, deposited by fast running water; sand, forming sandstone, deposited by slower running water, and silt, forming shale, deposited by slow running water.
At Dunns Swamp, there is a very thick layer of sandstone with no intervening layers of shale. As a result of earth movements, vertical cracks called joint planes form in the sandstone and cause it to break along these joints into roughly rectangular blocks. Water running across the joint planes erodes the rock more quickly than in the centre of the sandstone blocks, and the top of each block becomes a dome shape. Where two joint planes meet, weathering on the edges is more aggressive and the rectangular blocks tend to become oval in shape. Differential weathering patterns are created when differences in texture of the sandstone causes some layers to wear more quickly than others, generating the terraced appearance of the domes.
In some cases, usually by liquids seeping through the rock, sections of the rock are weakened and when those areas are exposed to the atmosphere, they weather more readily by wind action, forming caves like those at the western side of Dunns Swamp camping area. Eventually the cave will extend too far into the rock for the ceiling to support itself and the cave will collapse, forming isolated tilted blocks of sandstone, like those on the western side of the big pagoda on the western side of the Dunns Swamp camping area.
The swamp is not a natural phenomenon. It was established in 1923, by the building of a weir on the Cudgegong River, to provide water for the Kandos Cement Works.
Dunns Swamp, is located on the Cudgegong River in the Wollemi National Park, approximately 30km east of Rylstone. From Rylstone turn off at the hospital onto Narrango Road and follow the signs to Dunns Swamp. The road is unsealed but suitable for 2WD vehicles. There are toilets, picnic tables and wood BBQs but bring your own wood and water and take your rubbish away. Limited fee based camping is available at Gunguddy campground.