you have dirty minds,
probably when it was discovered they've seen a couple of locals having sex on the rock :blah:
Lol, no actually it is because it's a valley of giant penises
but maybe your theory is proved right these days
Nature has a wonderful sense of humor
They were actually created by vulcanic ashes, on top of which a lava stream flowed. Because the ashes erode more quickly than the lava, shapes like this came out.