Kent Spicer

-257.91074 x and 68.0 y 118.05701 z is the most common, tho is appears elsewhere as well.
And remember that is appears to be random, it does not appear every time.
Also here is a link to a discussion on the minecraft forums about this where a few people have posted more pictures
http://www.minecraftforum.net/forums/minecraft-discussion/discussion/2135237-new-generated-structure-mine

I believe this to be a glitch.