Natural?

Eli and Noah and I saw a picture of a canyon, it might have been the Grand Canyon, I don't know, but it was a beautiful picture. 

"Isn't that amazing?" I asked them.

"Yeah, that's really neat.  How is it like that?" Eli asked.

"It's all natural.  Over a long long time the water wears away the rock and cuts it down.  At the bottom is the river that washed it away," I explained.  "I'd like to go there sometime, I'd like to take you boys there for a vacation.  Wouldn't that be cool?"

"Yeah!" they both say.  Then Noah continues on, "So it's natural?  People didn't do it?" he seems a little unsure.

"Nope, it was all the water.  Isn't that amazing?"

"So, the river made the faces of the presidents?" he asked, with a little smile.

"Oh, no!  I didn't realize you were thinking of Mt. Rushmore!"  Eli and I laughed a little here, and so did Noah, so he might have been yanking my chain.  "Yes, people did carve that out of rock, but the canyons are made by rivers.  I'd like to see Mt. Rushmore too, wouldn't you guys?"