Ever since Pete Carroll bolted for the NFL, the reputation of West Coast college football has rested largely on the 560 miles of freeway between Eugene and Palo Alto. That balance seems far less stable in 2015.

Stanford already took a step back last fall, notching single-digit wins and missing out on a major bowl for the first time since 2009. A once-vaunted defensive line then lost a trio of fifth-year seniors, including All Pac-12 first-teamer Henry Anderson — a third-round NFL draft pick. The Cardinal went without a 1,000-yard rusher for the first time in seven years, and only return two players who ran for at least 300.

• Related: What to know about 2015 season

• Pac-12 preview: Is USC back on top of the South?

Oregon still looks like a potential playoff contender, with a backfield that can stack up against just about anyone in both talent and depth. But the absence of quarterback Marcus Mariota already offers opponents something they often lost by halftime: confidence.

But the bottom half of the division combined to win just seven conference games in 2014. Maybe the Ducks can sleep easy after all.

The coach who must win

Sonny Dykes quintupled his win total in his second season at Cal, but that feat isn’t particularly impressive considering that he debuted with a 1-11 record in 2013. The 45-year-old has been able to craft potent offenses, but thus far in his career, any gaudy numbers there are often undone by defensive sieves. Bears quarterback Jared Goff is a potential first-round NFL draft pick; if Dykes can’t at least get to a bowl game with him, his job could be in jeopardy.

Biggest impact freshman

Oregon State lost both its longtime head coach (Mike Riley) and the conference’s career passing leader (Sean Mannion). The transition might turn out to be smoother than anyone expected. The Beavers pulled Gary Andersen away from Wisconsin, and might have found a gem in dual-threat quarterback Seth Collins. Only a two-star recruit according to both Rivals.com and Scout.com, the 6-foot-3, 171-pound athlete flipped from San Jose State and enrolled early at OSU. His skills fit Andersen’s spread offense, and his spring camp performance might have made him the favorite to start.

Key early season indicator

How good is Oregon’s starting quarterback? The Ducks have been the conference’s standard-bearer in four of the past six seasons, losing out on a league title only when Stanford edged them in 2012 and 2013. Now that Mariota has moved on to the NFL, Oregon might be vulnerable again. The offense has plenty of playmakers, but a lot rides on the transition of former Eastern Washington star Vernon Adams — who will try to win the starting job despite not having been in Eugene for spring camp.

2015 College Football Preview

• USC vs. UCLA Predictions: Who will win the rivalry game?

• Could Adoree Jackson wins the Heisman and an Olympic gold medal?

• What does Josh Rosen need to do to succeed as freshman QBs?

• A look at the road to College Football Championship

• Games to watch: Preview of each week’s best game

• What to know about 2015 college football season

• A look at Scott Wolf’s pre-season rankings

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