Arizona League
The team first competed in the Arizona League (AZL) in 1988, as a cooperative between the Seattle Mariners and the Boston Red Sox known as the Arizona League Red Sox/Mariners. In 1989, the team became an affiliate solely of the Mariners, and was renamed as such. The team has operated continuously in Arizona since then. Prior to the 2021 season, the Arizona League was renamed as the Arizona Complex League (ACL).