the bumper boulders

There’s 2 questions here.

One.
Why are these boulders rubbed smooth on their sides?
There’s no rain or rivers here.

Two.
How did these boulders move to the valley bottom.
There’s no rain or rivers here.

They’ve been jostled side-to-side by earthquakes. Yes, grinding against each other —ten ton dancing raindrops pushed over the desert floor more than a million years. Neato. Nifty. Wow.

Surfed a seismic wave lately?