It is located in Citrine Mountain start by going to the Citrine Mountain from the Abandoned Power Plant and get to this Rock Climb place.

After that go up the Rock Climb spot and go down into the ladder you will then reach another part of Citrine Mountain with an exit to the Celestinine Cascade and a river to the right, start surfing on the river and go down the waterfall, you will reach an area with a few Mining Rocks and hidden items, get to this area and push the strength boulder.
The Skuntank will be in the left along with a purple Key-Card that can be used on the Card Reader in Coreys Room in the Beryl Gym to open a secret room with a Toxic Orb, a book with a last message to Heather and Field Read-Out 11 for the Corrosive Mist Field if you didn't have it already.
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