So, who's seen anything at all like this? ALIENS???
I come out to go to work and find this pile of gravel near the wheel of the truck. Look closely, there's a gravel parking spot under the truck mixed in with those weeds there. Likely where the pebbles came from.
I'm guessing raccoons, which fed in the nectarine and apple trees there.
And there was another pile in front of the truck as I recall. And there's no kids in the area and the adults around there would have been too lazy to go to all that work:
The desert is a true treasure for him who seeks refuge from men and the evil of men. In it is contentment In it is death and all you seek (Quoted from "The Bleeding of the Stone" Ibrahim Al-Koni)