Minecraft wiki entry for Before_1.18, associated text: Giant spruce taiga hills were a variant intended to be a more mountainous version of the giant spruce taiga. However, in Java Edition, due to a likely error in the way terrain height is calculated, there was no difference in the terrain between giant spruce taiga and giant spruce taiga hills. Specifically, the game used internal values known as setBaseHeight and setHeightVariation when generating hills biomes, but these values were the same for both giant spruce taiga and giant spruce taiga hills, resulting in no actual difference between the two. This was the only hills biome in the game with this issue.[1]