Canyon Formation
Formation of the huge canyon (Valles Marineris) is also likely to be tectonic in origin. However, details are not very well understood. It was probably produced by horizontal stretching in response to some mantle processes. The canyon's existence suggests that the Martian surface must have experienced large-scale extension sometime in its history. Over the past billion years, however, the planet's surface has been compressing due to planet-wide cooling and contraction.

As a result, wrinkle ridges similar to those found on the Moon can be observed (Figure 7.3). In this image, sunlight comes from the left. Thus, it follows that the narrow curved feature next to the upper left edge represents a rift valley, and the remaining elongated structures are elevated ridges on the Martian surface.