You wouldn't know it by the temperatures in the 70s, but this is late October. The leaves are turning colors, and the college football conference races are turning serious.

Nowhere is that more apparent this week than State College, Pa., where No. 2 Penn State begins a challenging three-game stretch that not only will weigh heavily in the Big Ten race, but also will have a big say in the national championship and Heisman Trophy chases, too.

The defending Big Ten champion Nittany Lions (6-0, 3-0 Big Ten) play No. 19 Michigan at Beaver Stadium on Saturday night, then travel to No. 6 Ohio State and No. 18 Michigan State in consecutive weeks. Should Penn State survive that gantlet unscathed, the team will be well on its way to winning the Big Ten East and meeting likely West champ Wisconsin in a rematch of last year's stirring conference title game.

Nittany Lions coach James Franklin wouldn't bite when asked about the tough stretch and other non-Wolverines subjects.

"Let's start talking about Michigan, Michigan, Michigan, Michigan, Michigan, Michigan, Michigan, Michigan, Michigan, not the white-out, not the rankings, not last year's Big Ten championship, not any of these other things," he said.

OK, Coach. Here ya go.

Michigan (5-1, 2-1) enters the game with the Big Ten's top defense (223.8 yards allowed per game) and will try to harness Penn State running back Saquon Barkley, the Heisman Trophy front-runner whose 217 all-purpose yards per game leads the nation. The Wolverines did so, to a point, last year in a 49-10 beatdown of the Nittany Lions in Ann Arbor, limiting Barkley to 136 yards from scrimmage (59 yards rushing).

"I've been doing this for 23 years at every level, including the NFL — I can't imagine that there's a better running back and playmaker than him," Franklin said of Barkley, who has rushed for six TDs, caught two TD passes, returned a kickoff for a TD and thrown a TD pass. "That's no disrespect to Bryce [Love, Stanford running back and the nation's leading rusher]; he's obviously a special player as well. … Being able to use [Barkley] in so many different ways to get the ball in his hands, it allows us to make sure he's going to have an impact each week and I think causes some headaches for defensive coordinators."

This week's headache will belong to Michigan defensive coordinator Don Brown, a colleague and counterpart of Franklin's when both were coordinators at Maryland. Franklin expects a stiff challenge.

"I mean this as a compliment — Don's a greedy defensive coordinator," Franklin said. "Most defensive coordinators are going to take something away while giving you something else [schematically]. … Don doesn't want to give you anything."

Michigan will need that stout defense Saturday night because nearly 107,000 are expected to cram their way into Beaver Stadium. "It's as impressive as any place I've ever been," said Michigan coach Jim Harbaugh, who's making his second trip to Happy Valley. "It's a great atmosphere for football. … As far as simulating that environment, we're going to make loud noise at practice."

Even if Penn State does beat Michigan, next week's trip to Ohio State won't get any easier. The Buckeyes (6-1, 4-0) have recovered well from their puzzling home loss to Oklahoma, and they can thrust themselves back into College Football Playoff contention by beating the Nittany Lions.

Should that happen, there's this interesting scenario for the Big Ten: CBS Sports' Jerry Palm, the best in the business when it comes to bowl projections, has both Ohio State and Penn State in the playoff — and meeting in the national semifinals in the Rose Bowl. Here's how it could happen: The Buckeyes beat the Nittany Lions in a tight game next week, and then run the table, including the Big Ten title game. Meanwhile, Penn State rebounds to win its final four games, finishing an attractive 11-1.

Will it happen? Too early to tell, but these big conference matchups sure make for fun speculation.

Randy Johnson covers college football for the Star Tribune.

rjohnson@startribune.com

Twitter: @RJStrib