Located in Waterloo, Iowa, the Waterloo Diamonds were a baseball team that formed in 1989 and lasted until 1993. A member of the Midwest League, they were affiliated with two teams in 1989-the Baltimore Orioles and San Diego Padres. From 1990 to 1993, they were affiliated solely with the Padres. Their stadium was Riverfront Stadium.
Waterloo Diamonds Wikipedia
(from Baseball Reference)