On Mars there is a really wonderful canyon. Well, more like a system of chasmas and enormous depressions...about 4,000 kilometers (2,500 miles) long, roughly along the equator.
That's about as far as from Cadiz to Helsinki. Or Seattle to Philadelphia. Or Perth to Sydney.
This image below of this canyon, called the Valles Marineris, looks north over the central part.
That's Melas Chasma in the foreground, behind is Candor Chasma, and the steep walls of the Ophir Chasma are at the top.
They range from 5 - 7 kilometres (3 - 5 miles) deep.
Here's a zoom in:
As on Earth, we can see faulting, landslides and layered deposits. The layers would indicate to me either water sedimentation, wind deposition, volcanic activity or all three.
For a really nice high dpi view of this, go here.