The trial site is located at the north end of the canyon. The trial begins once the player enters the trial site; they can leave the way they came in at any time, although this will reset the trial. If the player loses the battle against the Totem Pokémon, when they attempt the trial again they will only need to battle the Totem Pokémon; however, if they then leave after this, the trial will be reset. The player cannot use Charizard Glide during the trial.
This is a natural trial that has no Trial Captain, said to be the first ever trial. A tablet at the entrance of the trial site explains the trial. The player proceeds forward through the trial site, being attacked by a wild Jangmo-o and a wild Hakamo-o that leap from up high as the player proceeds toward a Z-Crystal pedestal. If the player tries to proceed out of the passageway behind the pedestal, they will be forced to turn back due to the fear that the Totem Pokémon will attack them from behind. When the player attempts to take the Z-Crystal from the pedestal, they are unable to retrieve the Dragonium Z before being attacked by the trial's Totem Pokémon, a Kommo-o.
In the battle with Totem Kommo-o, it will call Hakamo-oSM/NoivernUSUM on its first turn, and call Scizor if its HP is below 2/3 (if the ally Hakamo-oSM/NoivernUSUM has been defeated). If its HP drops below 2/3 before it has a chance to call an ally, it will call Scizor first, then call Hakamo-oSM/NoivernUSUM at the first opportunity after Scizor has fainted. Once an ally is defeated, Totem Kommo-o cannot call it again.
After completing the trial, the player collects the Dragonium Z from the pedestal.
Vast Poni Canyon first appeared in Family Determination!, where Lillie and Gladion traveled through it on their way to the Altar of the Sunne. Along the way, Lillie constantly kept seeing obstacles in their way, such as thinking that two cliff-sides would have an invisible bridge in between them, and thinking up ways to solve said obstacles, only for her assumptions to be proven wrong by Gladion. In the final cave before reaching the altar, Lillie and Gladion came face to face with a TotemKommo-o and its army of ally Jangmo-o and Hakamo-o. However, with Gladion changing his Silvally into a Fairy-type, the Totem Pokémon was quickly defeated. Soon after, the two were joined by Ash, the rest of Lillie's classmates, and Professor Kukui.
The canyon reappeared again in Evolving Research!, where Sophocles traveled there in order to evolve his Charjabug. In the canyon, he encountered Horacio, who was also trying to evolve his ShinyCharjabug. Horacio claimed that there was a special evolutionary stone in the canyon called the "Bug Stone" that could evolve any Bug-type Pokémon. Sophocles subsequently challenged Horacio to a contest to see which one of them could evolve their Charjabug first. When Horacio tried to cross a plank bridge to get to the Bug Stone, the old bridge broke under his feet, leaving him hanging for dear life on one side of the canyon. Sophocles's Charjabug then evolved into Vikavolt, saved Horacio, and retrieved the Bug Stone, which Sophocles gave to Horacio, since his Charjabug had already evolved. However, much to Horacio's dismay, the stone had no effect on his Charjabug whatsoever, and Sophocles revealed that it was actually the special magnetic field present in the canyon that causes Charjabug to evolve. Afterwards, Horacio swore to evolve his Charjabug through training and then challenge Sophocles to a Vikavolt race once he had done so.
Vast Poni Canyon first appeared in the Sun, Moon, Ultra Sun & Ultra Moon chapter. It is the site where Hapu's deceased grandfather was buried. After becoming the Kahuna of Poni Island, Hapu set off to visit her grandfather's grave and show him that she succeeded him as the next Kahuna. After seeing how much Hapu loved her grandfather, Sun decided to join her.
Later, Faba and a group of Aether Foundation Employees arrived at Vast Poni Canyon. Faba sent some Employees off to capture Hapu so he could interogate her while he and the remaining Employees went to the Altar. There, Faba was attacked by Plumeria, who demanded that he tell her where Guzma was taken to after being kidnapped by a Nihilego. Afterward, Faba was approached by Moon and Anabel, who wished to know about the Aether Foundation's involvement with the Ultra Beasts that had appeared in Alola.