The colours of Rainbow Valley formed between 80 and 20 million years ago, when
central Australia had a warm wet climate.
During this period there was
abundant underground water, which dissolve small quantities of iron and silica
from the sandstone.
During dry periods, the evaporation of water from the surface caused the
underground water and dissolved minerals to be drawn upwards by capillary
action. The minerals were deposited at the surface, where the iron formed a
thin, colourful veneer over the quartz grains in the sandstone. The silica
became a strong cement binding the grains together.
The process, known as laterisation, has helped shape the landscape at Rainbow
Valley. The coloured zones form a hard capping that protects the softer white
rock from erosion by wind and rain.
Source: NT Parks and Wildlife signage