JEFF HALLER/Yakima Herald-Republic Prosser's Ivan Merino runs the ball on a drive late in the first quarter as Prosser plays Ellensburg in Ellensburg Thursday.

ELLENSBURG — Year after year, the personnel changes and most of the faces in the red helmets are new.

But the legacy of Prosser's dominance in Mid-Valley League football has endured, the tradition now spanning three decades.

And on Thursday night at Andreotti Stadium, the current caretakers of that legacy were as impressive as any, defeating Ellensburg 48-12 to finish unbeaten in league and sweep aside the Bulldogs' hopes of forcing a three-way tie for the title.

The victory marked the 12th time in 16 years that Prosser has run the table in the Mid-Valley, and since moving up from the Valley A League in 1989 the Mustangs have an astounding 106-5 record in the league.

"It's a tradition every team always wants to carry on, so when it's your turn you have to take care of it," said senior tight end Jorgen Gilbertson, who scored Prosser's first two touchdowns. "I guess they just breed us different in Prosser. There's a big expectation to win, but we thrive off that."

With the Mid-Valley's No. 1 seed into the postseason, the second-ranked Mustangs (6-0 league, 10-0 overall) will host Clarkston (4-6) at 6 p.m. Tuesday in the regional playoffs.

West Valley defeated Wapato on Thursday to secure the Mid-Valley's second regional berth, and the Rams (9-1) will travel to East Valley of Spokane on Tuesday.

Right from the start on Ellensburg's frigid turf, Prosser was relentless, scoring touchdowns on five of its first six possessions and dashing off to a 35-0 lead at halftime. It was 42-0 heading into the final quarter.

Gilbertson, who also starts at middle linebacker, follows his two older brothers, Nate and Jens, who wore the same No. 8 and starred as wide receivers. A league championship — and an unbeaten one at that — wasn't something Jorgen planned on missing.

"That's been our focus, but we're not done yet," he said. "Today we wanted to come out strong and hit them hard early. We played a great first half."

That first half was impressive for Prosser on both sides of the ball.

Sophomore quarterback Kellen Moore threw four touchdown passes, including the first two to Gilbertson from 11 and 22 yards, and the defense held Ellensburg to 26 yards on the Bulldogs' first seven possessions.

Moore completed 13 of 20 passes for 215 yards to surpass 2,000 for the season, and his four scoring tosses put him at 33 for the year.

"It's great to finish (league) like this," he said. "I grew up around Prosser football and it's great to be a part of it now. The guys we're really fired up today and we played a great game."

Running back Ivan Merino rushed for 161 yards on 14 carries and scored on a 65-yard sprint in the second quarter.

Merino's touchdown run sparked a three-score barrage that, in less than two minutes, included Moore's scoring strikes to Danny Lochrie (33 yards) and Bud Sexton (19) and put the Mustangs ahead 35-0.

Ellensburg, which lost 1,000-yard running back Josh Kopczynski to an injury last week, got 116 yards from his replacement, junior Luke Yarwood.