Photography

Yeah, it's pretty cool. Mangroves do something similar in coastal waters. As they grow bigger, they trap sediment from the water, which builds mud islands over time.

These particular creosotes are pretty old, and on the edge of the dune field there is always some blowing sand. When it hits those thickets of leaves and branches, the sand falls out of suspension. Over time it accumulates. The sides of those hillocks are studded with old dead roots and stems sticking out, which fertilize the sand, and the hillocks are riddled with small animal burrows, which also eat the seeds, help disperse them, and poop nearby. It's a mini-ecosystem!