Where the Walls Stand Up

Polly flew into the canyon. The walls were much bigger now. The red rock went straight up. There was no way to climb it.

Dark lines ran down the wall. They looked like black ink. But they were not paint. Water and dust made them, very slowly, over a long time.

Under the rock, Polly found many small nests made of mud. Hundreds of swallows lived there. Ride the wall, one bird said. The warm air goes up.

So Polly rode the warm air. She did not move her wings. That evening, the cliff was more than a thousand feet high.