A grouping of schools from the same basic league or cross leagues done by sport.
Supplemental leagues can change annually by agreement of all the schools and leagues involved.
Homestead Lynbrook Capuchino Jefferson Pioneer Piedmont Hills Mt. Oak Grove Valley Christian Westmont Saratoga Mtn. Lynbrook Carlmont Terra Nova Pioneer Lincoln Silver Creek Monta Vista Mtn. Sequoia Piedmont Hills Valley Christian Silver Creek Mtn. Moon Bay Santa Teresa Oak Grove James Lick Los Gatos Mtn.