Final answer:
The Valles Marineris on Mars is a vast tectonic fracture system resembling a rift valley rather than a traditionally water-carved canyon. These features were formed by crustal tensions associated with the Tharsis uplift and have been shaped further by erosion from wind and occasional water from deep springs.
Step-by-step explanation:
The Valles Marineris on Mars is the most striking example of a canyon system, though calling it a canyon can be misleading. These formations were not carved by running water like terrestrial canyons but are in fact large tectonic fractures that occurred due to crustal tensions from the uplift of the Tharsis region. The Valles Marineris extend for approximately 5000 kilometers and are up to 100 kilometers wide and 7 kilometers deep, sufficiently large to fit the Grand Canyon within one of its smaller chasms.
Despite the term "canyon", the formation of Valles Marineris is more closely related to rift valleys on Earth, caused by the pulling apart of tectonic plates. The initial tectonic cracks on Mars later experienced erosion with water from deep springs and today primarily by wind. These processes widened the cracks into the vast valleys we observe now, with features such as landslides adding to their complex morphology.
Therefore, the Valles Marineris is the most striking example of a canyon system evolved mainly due to tectonic activity, with subsequent wind and water erosion shaping the formation, correctly categorized as a rift valley.