Where do these splatmap textures come from? Are they generated by CTS or by Unity? EDIT: Been digging and still not sure where terrain.terrainData.alphamapTextures comes from. I wrote some debug scripts and a stock Unity terrain doesn't have any. Length of the array is 0. It isn't until I "Add CTS to Terrain" that the array length becomes 4 (on a working tile) but I can't figure out where in CTS they are getting set. This is definitely an area of Unity where I'm not very comfortable but I'm trying to dig through it to figure out what is breaking.