Desert

Deserts are sandy areas which spawn desert monsters, cacti (as of Patch 1.05), and waterleaf. Deserts are filled with sand and there is no wall behind it. If ores are found within the sand layer of a desert, then below them will be a dirt wall going from the Underground layer up to the ore as if to hold it up.

Deserts are also a good way to collect sand, as you can go to the bottom of the sand layer and hold your mouse button down with your pickaxe pointed at the bottom of the sand. It will then fall onto the place where your pickaxe is pointed, so you will get all the sand above it.