When I logged back in to my Minecraft single player world I was shocked to see that a quarter of an old build of mine was destroyed. It appears as though a new chunk was loaded into a previously loaded chunk. The biome should be extreme hills, but it says taiga hills.(Included screenshots to show biome differences. Also included a terribly positioned screenshot to show what the exterior looked like before the problem occurred.) I have been playing on this world since June 25, 2013 when Minecraft was still version 1.5.2 and my build is right next to my spawn area, but for some weird reason a new chunk appeared in an already loaded chunk. I have no clue as to what happened or what caused this to happen, but I'm not content because there were 8 or 10 saddles and an iron horse armor in the area that have disappeared. I don't keep backups so I guess I have to manually fix it. My world is on survival, so I can't hop on to creative mode. Sorry for the vague information, but i hope you can find out what happened so that no one else has to go through the same experience as me. I mean I know it wasn't a great build, but cut me some slack it was my first build and you didn't have to drop a chunk of land on top of it.
I just remembered I was farming new trees around that area. I needed more Acacia and Dark Oak saplings and wood, so I was growing some saplings with bone meal around that area. I don't know if that was the cause of this issue, but i thought I'd throw that out there. Sorry for the ridiculously long description, but this was my first and thank you for taking the time to read this.