Sylas' visualization had never been good at looking through barriers. Even when he was in the ocean, it was highly limited by the waters alone. In this situation, even with how porous the sand was, he couldn't see more than a meter or so underground.
However, that was enough for him to realize something.
The world around him was basically being held up by a large root system. The sparse trees might as well have been on an organic system, connected with one another, sharing resources and water. And it was because of this thick, continuous connection that the sand had anywhere to rest. But if one wasn't careful, it was easy to accidentally slip and fall into this endless network of roots.