Los Osos was the race victor in 47.37.
Niederhaus also competed in the 800 open run and finished fourth in her heat and 13th overall in 2:16.21 as Otay Ranch's Carina Gillespie captured the race in 2:13.60.
Vargas took seventh in her heat of the open 400 in 61.24, which was 23rd-best overall.
Claremont's Mariella McCormack won the event in 56.51.
Niederhaus, Vargas, Montgomery and Hailey James then completed Sacred Heart's effort by clinching ninth in their heat and 32nd overall in the open 1,600 relay in 4:12.53.
Carson turned in a winning time of 3:55.83.
Flintridge Prep's Kate Kennedy was her school's lone representative and partook in the open 300 hurdles, ending seventh in her heat and 21st overall in 46.34.
"I wanted to PR today. My PR was 45.3, so I didn't get it," Kennedy said. "But I'm going to keep on trying and will keep that as my goal."
Salesian 3, Flintridge Prep 0: Kory Hamane had nine kills and Kareem Ismail added eight on Thursday for the visiting Rebels (8-10) in a 25-13, 25-18, 25-20 nonleague defeat.
Village Christian 7, La Cañada 6: The Spartans dropped a nonleague game with the host Crusaders late Thursday two days after defeating Village Christian with a walk-off hit in the eighth inning.
La Cañada (8-8) led, 6-3, in the sixth, but the Crusaders poured on four runs in the bottom of the sixth for the one-run win.
The Spartans managed to out hit Village Christian, 9-6.
La Salle 6, St. Francis 4: It took a while, but the Golden Knights finally got to La Salle starting pitcher Bowdien "Bubba" Derby in the bottom of the six inning, scoring twice to cut a four-run lead to two.
St. Francis couldn't complete the comeback in the Arcadia Invitational Wednesday, though, as Derby settled down to end the inning and finish the seventh to complete the victory.
David Olmedo-Barrera notched a single and double in the game for the Golden Knights, who also got a two-run double for Cole Ramseyer, a single from Anders Schraer and a double from Tei Vanderford.
St. Francis 202, Crescenta Valley 210: Johnny Brandt carded a three-over-par 39 on Wednesday to share medalist honors with Nathan Han and push the Golden Knights (7-6) past the Falcons at Brookside Golf Course No. 1.
Jack Tenney and Michael Mozilo turned in 40s for St. Francis, which also got a 44 from Vince De Pinto.
Village Christian 218, Flintridge Prep 244: Jack Bouchard shot an even-par 34 on Wednesday for the Rebels (5-6) in a nonleague match at Chevy Chase Country Club.