red colour of the dunes is due to the “ferrogination” of the “haemitite” (the principal form of iron ore; consisting of ferric oxide in crystalline form). Ferrogination describes the action of iron coating the loose sand grains with iron rich material and getting oxidized over a period of time. Just like a nail exposed to salty air would get corroded and appear red in colour. By no means is this explanation of the process that caused the red hills definitive. There are other schools of thought by different geologists and the site still draws geological interest. That is why it is even more important that these dunes be preserved in its original form for future generations to admire and study.
They are unique because of the rarity of such gullied red dunes formations of which only three remain in South East Asia. These were formed over thousands of years.
On the Bay of Bengal coast, to the south of the Bheemunipatnam ridge, is an area comprising deeply gullied red sand dunes of around 4 km length and 2 km width You can look it up in Google Earth at (17 52.078' N, 083 25.845 E). This area is referred in Telugu as "Erra Matti Dibbalu" which translates to ‘Red Sand Hills’. It is bounded by streams “Chittigadda” in the North-West and “Peddagadda” in the South-West.
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Visakhapatnam, Andhra Pradesh