Science doesn't know where rocks come from. I do.
Thanks to the inconsistent gravity in the Asheville area, rocks often arrange themselves in strange patterns and display behaviors not exhibited by rocks in other parts of the world. For example, they arrange themselves into male and female arches and mate to create new rocks. One day last week, I walked down to the River to find this: 
The females can be quite aggressive ...
I now recognize this as a young female arch letting other rocks in the area know that she is available. I didn't see it happen, as I had to go up to the house to check on my jambalaya, but when I got back I found that some rocks had indeed answered the call and created a male counterpart:
He looks right excited at the prospect, aye?
After dinner I came back to find that the rocks had formed entirely new arches and had gone for a bit of a walk downstream, like two lovers out for a stroll: 
Ahh ... courtship. They say falling in love is the best high of all ...
The next day, after work-work, I went down to the River to find that those two arches had moved in together, now sharing a rock A on the other side of the River:
This is getting serious ...And finally, on Saturday morning, I went back down to the River to find that these two groups of rocks, whom had never met before a few days ago, had formed themselves into arches and completed the mating ritual. This never before seen material could be shocking to some viewers; parental discretion is advised: 
We have penetration!
As hard, heavy and rough as they are, rocks have a tender way of making love. Isn't that sweet?
The next day I went down to the River to find that they had left a pile of rock eggs that, over time, will grow into the rocks and boulders we see in the River: 
Just think, each will grow into a stackable rock ...
I think the rocks have a deal with the fish to look out for the young rocks until they are of a certain size (the rocks; not the fish). But I have no evidence to support that hypothesis.
Now that you know where rocks come from, spread the word.