|Friends:||Ash, Iris, Cilan, Ferris|
|First Appearance:||A Restoration Confrontation! (Part 1)|
|Voice actor:|| Samia Mounts (English)|
Minako Kotobuki (Japanese)
Season 15: Rival Destinies
When Sierra was younger, she, along with Ferris and two of their friends, were part of an amateur archaeology club.
She, Ferris, and a few of their friends often played in the off limit area of Twist Mountain and were all part of a detective group. Each wore a special pendant that symbolized their membership.
One day Ferris got lost while they played and they eventually found him unconscious which ultimately caused Sierra to be more respectful of the rules. She was convinced that it was only a dream he had. Once Team Rocket stole the Cover Fossil Ferris had found and he and Ash went after them alone, Sierra followed behind them in a truck along with Iris and Cilan. After they had escaped Team Rocket's helicopter, she picked them up and drove away from the scene.
Sierra would later trust Ferris' story after meeting Tirtouga and seeing the Time Gate for herself.