Since the ice ages, sea levels have receded and the old alluvial fans have been exposed to the erosive forces of wind and water which have weathered away the conglomerate. In some places this conglomerate is protected from erosion by a cap of cemented silt or rock; this has resulted in the formation of spectacular pinnacles, many of which have prominent fluting caused by rainwater running down their sides during major storms. It is not known exactly how long the pinnacles have been forming but they are thought to be less than 125,000 years old; major erosion probably began 7000 years ago and accelerated in the last 1000 years with the deforestation of the area.
For millions of years, sea levels have dropped, revealing ancient river fans that have been worn away by wind and water. In some areas, a layer of compacted sediment has protected the conglomerate from erosion, resulting in impressive pinnacles with distinctive fluting caused by heavy rainfall during severe storms. The age of these formations is uncertain, but they are thought to be less than 125,000 years old; erosion probably started around 7000 years ago and intensified in the last 1000 years due to deforestation.