Playing at Del Norte, Sundberg shot a round of 94 to pace the field by five strokes and moved four strokes clear in the league standings.
The defending league champion had placed third on opening day, but responded to move clear of the chasing pack with a big second round.
The Tigers stretched their advantage in the team standings with another dominating performance that saw them place six golfers in the top 10.
Iris Conrad led Arcata and shot a 101, which was the third best round of the day, with teammates Sagen Sarchett and Madyson Nelson tied for fourth one stroke back.
Arcata’s Avery Meadows and Amaya Urquidez and Eureka’s Gracie Christian each shot a 104 to tie for sixth, while Arcata’s Morgan Ford and Eureka’s Mia Lopez each shot a 105 to tie for ninth.
Sophia Jagger led Del Norte with a 113, Allyson Hagler led St. Bernard’s with a 121 and Kylie Ward had the best Fortuna score with a round of 128.
As a team, Arcata shot a 409, followed by Eureka (426) and Fortuna (473).
A big thank you to Baywood Golf & Country Club for helping to sponsor this year’s high school coverage.