Marcia is a Soc who was friends with Cherry Valance. She was dating a Soc named Randy, who was Robert Sheldon's best friend. Her birthday was May 24th. They show her in the movie when Dally, Ponyboy, and Johnny go into the nightly double to watch a movie when they see two girls sitting in the front row and Dally decides to annoy them.
Marcia was described as being kind of fat, with short dark hair.
Marcia, according to Dallas, barrel raced at rodeos with Cherry. She seems to be as wise-cracking as Two-Bit, and a little bit flirty. Her friendship with Cherry seems to go only as far as that their boyfriends are best friends.