It was a simple moment for Walker to sense the densest earth mana. He was surprised that it was in such a small area yet affected a larger area. Then again, it wasn't just the largest amount of mana that could cause issues in an environment. It was the density of mana as well.
Dense mana of any form could cause space to warp or cause either manas to react poorly. A dense droplet of water mana dropped in to a fire could still put it out and cause a burst of sparks to fly away in the process. It was just about how the mana was used and in what density at times.
The forest elves who had come to escort them wet emit fools, they understood that Walker knew exactly where the disturbance was. His mana sensing and control is high enough. However, they were very glad to see him using the tree walking skills to move through the forest.