Minecraft wiki entry for Windswept_Hills, associated text: The windswept gravelly hills variant replaces the top few layers of stone and grass with gravel across its landscape. Due to the gravel replacing most of the grass, trees generate far less often, making this variant relatively barren. Players should be careful when surfacing from underground in this biome, as the top layers of gravel can pose a suffocation hazard. This variant generates in lower humidity values, mainly next to plains and snowy plains.