Why are are rods, disks, spheres and rollers (Types of pebbles) distributed on a pebble beach like they are?

The rocks come from the rivers. Just look at all the wood that piles up during the rainy season even though there might not be any trees around. The beaches require rivers. If you dam up the rivers, the sand and rocks get washed out to sea. In California you will see man made rock formations that are there to trap the sand, because of the daming of the rivers. So basically the rocks were worn down when they were in the river, a rain came and washed them out to sea. The waves came along and pushed the sand and rocks against the shoreline and the scene repeated itself till the beach was formed. The waves come in on an angle so the push the sand down the coast. That's why you can have sand far away from a river.