In dry northwestern Peru, unusual 19-mile-long sandy (coastal) ridges were formed through tectonic activity, El Niño storms and natural sediment deposit. The nine ridges still standing appear to have formed from 5100 years ago until about 400 years ago. And they're topped with deposits of shells, rocks from fire pits and other human artifacts.

Scientists studying the (region) found that the shells are from mollusks and barnacles, and primarily of species still fished there today. They thus concluded that the shells were left by native communities who long called the region home.

The researchers also found that the clamshell and fire deposits (stabilized) the ridges and protected them from erosion. No such stable ridges exist along the coast from the past 400 years, after the local people died from disease or war, or were pushed inland. Any incipient ridges since were easily toppled by wind and storms.

The research is in the Proceedings of the Natural Academy of Sciences. [Daniel F. Belknap and Daniel H. Sandweiss, Effect of the Spanish Conquest on coastal change in Northwestern Peru]

Visitors now see what they may think is a natural (landscape). But its formation depended on thousands of years of human activity.