From Bulbapedia, the community-driven Pokémon encyclopedia.
Grampa Canyon (Japanese: グランパキャニオン Grampa Canyon) is a location in the Pokémon anime. It is found right outside of Neon Town.
When Ash and his friends were traveling through the canyon in Attack of the Prehistoric Pokémon, they learned that some ancient Pokémon Fossils were found recently. Along with Gary, the kids began digging in the canyon to look for the Fossils. Meanwhile, Team Rocket had planned to blow up the entire canyon to collect the Fossils with dynamite, which would have placed several innocent bystanders in mortal danger.
Thanks to Team Rocket, Ash and Pikachu ended up in a hidden cavern found in the canyon. There, they found that five extinct Pokémon were living alive and well. They weren't happy about being disturbed, and eventually an Aerodactyl lifted Ash out of the cave. He was saved by his Charmeleon evolving into Charizard and battling it. As a result of the entire incident, paleontological work for finding any Pokémon Fossils was shut down indefinitely.
In addition to the ancient Pokémon, Ash also found an Egg in the canyon. It would eventually hatch into a Togepi that would imprint Misty as its owner.
Pokémon seen in Grampa Canyon