The Wood Gravel Wall is a building-block with light brown wooden floor-boards on four sides and dark-brown stucco with a wooden frame on two sides. It can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015), but only after the crafting-recipe has been unlocked upon taking/crafting a Stucco Wall for the first time (which is unlocked by taking/mining soft brown Canyonstone, found high up in Canyons-biomes, which will require a Stone Mining Cell or better).