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The Dorsa Argentea Formation (DAF) is thought to be a large system of eskers that were under an ancient ice cap in the south polar region of Mars. This group of ridges extends from 270–100 E and 70–90 S, around the south pole of Mars. It sits under the Late Amazonian South Polar Layered Deposits (SPLD), in the Mare Australe quadrangle. The amount of these ridges is huge, one study studied seven different ridge systems which contained almost 4,000 ridges that had a total length 51,000 km.
Most eskers are thought to be formed inside ice-walled tunnels by streams which flowed within and under glaciers. After the retaining ice walls melted away, stream deposits remained as long winding ridges.
Crater counts show that the ridges are of two different ages. One dates from Early Hesperian, while the other group dates to the Late Noachian. These dates correspond to the time when Mars had lakes and valley networks which formed from runoff, drainage and storage of liquid water on the surface of Mars.
The Dorsa Argentea Formation represents a time when there was melting and drainage of meltwater from a giant ice sheet around the Martian South Pole. Various mechanisms may have caused the ice to melt. Possible mechanisms may have been a warmer atmosphere, volcanism, or increased thickness of the ice cap from accumulating snow.
MARSIS radar data suggest that significant areas of layered, potentially ice-rich parts of the Dorsa Argentea Formation remain today.