The return of Ivan Rabb makes Cal a challenger in the Pac-12. USATSI

The Pac-12 had a breakthrough season last year which saw seven teams reach the NCAA Tournament.

Will that trend continue moving forward?

Check out our breakdown below as we take a look at five offseason storylines in the Pac-12.

1. Ivan Rabb is a national player of the year candidate

Cal had as talented a team as nearly anyone in college basketball last season when everyone was on the floor and that limited Ivan Rabb's ability to have the type of impact that he was capable of.

Nevertheless, the 6-foot-11, 220-pound big man still could have left school after his freshman season and been a lottery pick, but opted to return to Berkeley and have a bigger role as a sophomore.

That's bad news for the rest of the Pac-12.

Rabb only averaged 7.7 shots attempted last season and still averaged 12.5 points and 8.6 rebounds while shooting an impressive 61.5 percent from the floor.

With Ty Wallace, Jaylen Brown and Jordan Mathews no longer in the Bears' program, look for Rabb to become a focal point and flourish for Cal in 2016-17.

The Oakland native could conceivably average 20 and 10 next season.

2. Oregon's chemistry could be a work in progress

Dana Altman has always been a master at solving personnel puzzles during his tenure in Eugene and it says here next season could be his toughest one yet.

The Ducks return five of their top seven scorers (Dillon Brooks, Tyler Dorsey, Chris Boucher, Jordan Bell and Casey Benson) from last year's team that won 31 games and lost to Oklahoma in the Elite Eight while also adding three players -- Dylan Ennis, Payton Pritchard and Kavell Bigby-Williams -- who all expect to have major roles.

Part of the reason why Oregon was so successful last year was because its role allocation was beyond concrete after Ennis was lost for the season with a foot injury in early January.

Now it remains to be seen how his return and the additions of Pritchard -- a top-50 recruit -- and Bigby-Williams affects a team that is the consensus favorite to win the Pac-12 for the second consecutive season.

3. Both Arizona and UCLA have rebounding questions to answer

The Pac-12's two most storied programs are both in position to be top-15 teams nationally, but need to prove that they can each hold their own on the glass.

UCLA suffered a loss up front last week when power forward Jonah Bolden opted to leave school to turn pro, leaving the Bruins with freshman T.J. Leaf and veteran big man Thomas Welsh (11.2 points, 8.5 rebounds in 2015-16) as a projected starting duo up front. Freshman Ike Anigbogu will now likely become UCLA's third big man following Bolden's departure.

Arizona meanwhile has always been exceptionally strong on the glass under Sean Miller, but following the departures of both Ryan Anderson and Kaleb Tarczewski, it remains to be seen how the Wildcats perform on the boards next season.

Those two players averaged a combined 19.4 rebounds a year ago and now new faces need to emerge up front for Arizona.

Junior big man Dusan Ristic is primed to step into a bigger role, but he's been someone up to this point in his career that's been more known for his offense than his ability to be nasty in the paint.

Six-foot-11 freshman Lauri Markkanen is another player that will have to contribute on the glass along with sophomore Chance Comanche and red shirt freshman Ray Smith, who missed all of last season with an ACL tear.

UCLA and Arizona both have the talent to compete for a Pac-12 title next season, but it remains to be seen which players will emerge as consistent rebounders for each of these programs.

4. The second half of the conference is wide open

Oregon, Arizona, UCLA, Cal and Colorado all look to be a cut above the rest of the teams in the Pac-12 on paper, but the order after that is hard to project.

Utah, USC, Washington, Stanford, and Oregon State all had significant departures following last season while Arizona State and Washington State are still in the process of rebuilding their respective programs.

If you took the teams that will be picked 6-10 in the preseason and flipped them, there's probably not a great deal of people that would argue about that potentially being a possibility at the end of the regular season.

The Pac-12 is a mystery after the top five teams in the conference.

5. Colorado looks like a sleeper

Tad Boyle has made the Buffaloes into a perennial NCAA Tournament contender and don't be surprised if next year's squad plays its way into the top third of the Pac-12.

Colorado lost a first-team all-conference player in big man Josh Scott, but returns arguably the league's most underrated core of wings.

George King (13.6 points, 4.7 rebounds in 2015-16) and Josh Fortune (10.3 points, 4.0 rebounds in 2015-16) are two guys that started last season while talented forward Xavier Johnson returns after missing last year with an achilles injury.

Add Derrick White, a former Division II All-American that sat out last season and Boyle has some serious options on the wing, one of which is to play Johnson in spurts at power forward -- a position where he has thrived at in the past.

Wesley Gordon and Tory Miller are back as two experienced big men while Dominique Collier and Thomas Akyazili also return to form a solid combo at point guard.

The Buffaloes may be under the radar but there's certainly the potential to contend in the conference.

Expect Boyle to boast one of the most complete rotations in the Pac-12 while leading Colorado to its fifth NCAA Tournament appearance in the last seven seasons.

This and That

  • Bobby Hurley again isn't holding back with Arizona State's non-conference schedule. The Sun Devils will play neutral site games against both Kentucky (Bahamas) and Purdue (MSG) while traveling to San Diego State and hosting Creighton. Arizona State will also play three games in the Puerto Rico Classic in November, where it opens against Northern Iowa.

  • Washington could again be the Pac-12's mystery team. The Huskies lost their top three scorers ---- Andrew Andrews, Dejounte Murray, and Marquese Chriss -- from last year's squad that reached the Postseason NIT, but return four players that averaged over 20.0 minutes while adding a one-and-done caliber talent in freshman wing Markelle Fultz.

  • USC needs quality minutes from freshman guard De'Anthony Melton if it wants to have a chance to return to the NCAA Tournament. The 6-4 Melton has glue guy type potential and needs to relieve some of the pressure that's going to be on Jordan McLaughlin to create offense following the unexpected departure of Julian Jacobs.

  • Looking for an under-the-radar breakout guy in the Pac-12? Try Stanford's Marcus Sheffield. The Cardinal need another scorer to emerge following the loss of Rosco Allen and Sheffield could be that guy. The 6-5 guard averaged 6.0 points last season as a freshman.

  • One nugget for basketball junkies to store: Oregon State's sophomore trio of Tres Tinkle, Stephen Thompson Jr., and Drew Eubanks may be as good as any second-year triumvirate in all of college basketball.

  • How many NCAA bids can the Pac-12 expect in the 2017 NCAA Tournament? Find out the answer to that question and others on this week's edition of the College Hoops Today Podcast.