What causes the even pattern of ripples in a “washboard” gravel road?

Question

I finally stopped to look more closely. These ripples are about 10 inches wide ands look to be almost exactly uniform through long stretches of road. Where does this precision come from?

In: 879

Answer 1

Ya hit a bump so ya bump.

But when the bump lands it makes a bit of another bump.

A few cars go by and the 2nd little bump is now a bump that when ya hit it makes ya bump.

But when ya land from the 2nd bump it makes a bit of another bump.

Keep it up and ya got a washboard.