Pat Noonan, Tommy Meyer, Rafael Garcia and Andrew Boyens also scored for the Galaxy. which finished the season 6-3-1.
"It's a tribute to how hard this team has worked," said Galaxy Coach Curt Onalfo, who got a Gatorade bath after the game. "We played a great brand of soccer and scored a whole bunch of goals."
The Galaxy led, 1-0, at the half on Noonan's goal before a rebound score from Meyer in the 55th minute opened the floodgates in the second half.
"I knew we would play well. All the guys were up for it," said McBean, 17, who has appeared in two MLS games. "But the result really showed how hard we've been working over the past couple of weeks.
"I think any one of us could step onto to the first-team field and compete and perform out there."
Two of the players the Galaxy used Friday -- forward Edson Buddle and Boyens, a defender -- have played in a World Cup.
The West Division title was the first for the Galaxy, which went 1-6-3 last season.
The West Division is one of three sponsored by the MLS. However the three division winners do not meet to determine an overall champion.