Valles Marineris, the grand valley of Mars named after the Mariner program which first took close-up images.
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Image from: USGS

Valles Marineris

Valles Marineris is a large system of canyons, shown in this image, that stretches 4000 km (2500 mi) along the equator of Mars. It was first imaged in detail by Mariner 9. The scene to the left (centered at: lat -8, long 78) shows the entire Valles Marineris canyon system, over 2000 kilometers long and up to 8 kilometers deep. This system extends from Noctis Labyrinthus (check the large topographic map of Mars) - the arcuate system of grabens to the west, to chaotic terrain to the east. As can be seen in the image, many huge ancient river channels originate at chaotic terrain, from north-central canyons in the image, and extend north. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible on the leftmost (western) edge of the image. To the south are the highlands; very ancient terrain, covered by many impact craters.

High resolution images returned by the Mars Global Surveyor spacecraft allow closer examination of this unusual canyon. These images show slopes descending steeply to the north and south in broad, debris-filled gullies with intervening rocky spurs.

Layered rocks on Earth form from sedimentary processes (such as those that formed the layered rocks now seen in Arizona's Grand Canyon) and volcanic processes (such as layering seen in the Waimea Canyon on the island of Kauai). Both origins are possible for the Martian layered rocks seen in Valles Marineris. In either case, the total thickness of the layered rocks seen in these images indicates that there may have been a complex and extremely active early history for geologic processes on Mars.

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