Eclo Canyon is first mentioned at the beginning of Pokemon Colosseum as the location of Team Snagem's hideout during a news broadcast. This implies that the canyon was able to hide the Snagem Hideout very well, as its location was only discovered because of the loud explosion.
In Pokemon XD, two travelers tell Michael that they were jogging in Eclo Canyon and they felt like there were people there, despite Team Snagem having supposedly abandoned their hideout. Eclo Canyon is located very close to the Cipher Key Lair.
Although Eclo Canyon is a commonly referenced area by NPCs in Pokemon Colosseum and XD, it itself is not an accessible location, only the Snagem Hideout is.