Anne M. Peterson / The Associated Press

The college football season opens next week, and as of Friday five Pac-12 teams had yet to formally name a starting quarterback.

Oregon State, Washington State, Colorado, Arizona and USC have not made their starters official. In some cases it may just be coaching strategy, but in others the competition is just too close to call.

The 25th-ranked Beavers fall into the latter category, with coach Mike Riley still trying to decide between Cody Vaz and Sean Mannion. It looked like a choice was coming last weekend, but then — nothing.

“I’m trying not to think about it,” Vaz said about the day-to-day uncertainty.

Mannion started Oregon State’s first four games last season but injured his left knee and required arthroscopic surgery. Vaz stepped in and won the next two games, giving the Beavers their best start since they also went 6-0 in 1907. Both quarterbacks were used the rest of the way as Oregon State finished a better-than-expected 9-4 and went to the Alamo Bowl.

Riley said he will probably use both players in the opener next Saturday against Eastern Washington.

“I know from a personal standpoint, everybody wants to be named ‘The Guy,’ right?” Riley told reporters this week. “And some would probably profess that it would make it better (to know the starter), that it would help them relax and play better. But this is not a game about relaxing, it’s a game about responding to pressure and playing under pressure.”

At No. 24 USC, coach Lane Kiffin still has not decided between Cody Kessler and Max Wittek, who are trying to succeed Matt Barkley.

While Wittek started the Trojans’ final two games last season, Kessler seemed to be a bit sharper than Wittek in spring ball and summer workouts.

“Ideally, we do want to have one quarterback for the starter for the opening game,” Kiffin said this week. “We’re not really a two-system-quarterback program, but at the same time we’ve got to make sure we find the right guy. So I would not rule out anything, but that’s the same thing I’ve said for three weeks.”

The Trojans open the season on Thursday night at Hawaii.

Arizona coach Rich Rodriguez said he may be forced to play two or three players at quarterback in the early games this season.

The Wildcats’ apparent front-runner is senior B.J. Denker, who saw some game action — including one start — as backup to Matt Scott last season. But transfers Jesse Scroggins and Nick Isham are also in the mix, along with freshman Anu Solomon.

The Wildcats host the Northern Arizona Lumberjacks on Friday night.

New Colorado coach Mike MacIntyre is also trying to choose between four candidates. While it appears that junior Connor Wood — who entered preseason camp atop the depth chart — is the leading candidate.

The Buffaloes open with Colorado State in Denver on Sunday, Sept. 1.

Probably the most puzzling of the unannounced teams is Washington State, where it appears that Mike Leach is just going to make season-opening opponent Auburn wait a bit longer to know for sure.

But junior Connor Halliday is pretty much a lock.

Halliday completed 52 percent of his passes for 1,874 yards, with 15 touchdowns. But he also threw 13 interceptions, many by forcing the ball into coverage. That may be why Leach has left the door open for freshman Austin Apodaca. Or maybe not. Leach is not saying.

California entered preseason camp with a four-way quarterback competition, but new coach Sonny Dykes declared late last week that freshman Jared Goff had earned the job.

The Golden Bears open the season at home next Saturday against Northwestern.

Goff joins the six Pac-12 quarterbacks whose jobs were already solidified: Oregon’s Marcus Mariota, Stanford’s Kevin Hogan, Washington’s Keith Price, UCLA’s Brett Hundley, Utah’s Travis Wilson and Arizona State’s Taylor Kelly.