Mesa Biomes should spawn much lower

The Mesa biome is gorgeous as it is, but if the gaps between plateaus were to continue generating below sea level to create river canyons like the Grand Canyon, it would look incredible. Spawn with an average depth of Y=30-40, and have some canyons spawn as low as Y=15. Imagine reaching the edge of a spruce forest and finding one of these flat mesa plateaus. At first you might not realize the flatness hides the sheer height of the cliff in front of you, but once you reach the edge you get a clear view of the surrounding canyon. It creates a clear route to explore, and you can walk along the edge until you find a way across. A fun addition to this would be to add an achievement for filling a canyon to sea level with water.