[Doctor Stochastic]

There isn't anything else like the Grand Canyon on Earth,...

There's the Barranca del Cobre. It's not like the Grand Canyon exactly; it's bigger and deeper and prettier.

Not to mention the Gorges du Verdon (a bit smaller.)

[Doctor Stochastic]

Seems like I left out:

Hell's Canyon
Cotahuasi (11000ft deep)
Yarlung Zangbo
Colca
Monterey Canyon (4000m deep)