Sierra is a chestnut pinto. She is a mustang cross and the mother of Rain. She was born into a herd run by Tally and Shadow. She loved how her mother was a white-coated mare. She often wandered around, and one day, this caused her problems as she led wolves back to her herd.

The herd lived, but Shadow was hurt, and a stallion started to follow the herd. The stallion soon won the herd from Shadow by kicking out the colts, Shadow and Paco. This new stallion kept trying to make the herd move and didn’t know much. Once winter came, he refused them to go to their grazing grounds, and made them go where he wanted. The herd grew hungry near winter’s end, and Sierra wandered off and got lost. She didn’t see any other horses until she saw humans fighting. Afterwards, she met Storm, a strange-smelling stallion.

He led her to the village. While he went in, she didn’t trust the men and stayed alone. Soon, she bonded with them. She still didn’t go into the village. It wasn’t long before she had a foal with Storm; as it stood, it started to rain, and she named the foal Rain. When Rain first saw her father and the humans, she ran around playfully. It is unknown what happened to Sierra after this.