Arizona - C Steven Gurrola
The 2014 second-team All-Pac-12 selection in the middle of the Wildcats offensive line will be tough to replace. A two-year starter, Gurrola has been crucial in paving the way for a ton of rushing yards for Ka'Deem Carey, Nick Wilson while protecting B.J. Denker and Anu Solomon.
Who might replace him? Carter Wood Sr. - Wood saw limited time behind Gurrola last year and is expected to step in as a full-time starter in 2015.
Arizona State - WR Jaelen Strong
A likely first round pick, Strong left after his junior season after amassing more than 150 receptions, 2,200 yards while catching 17 touchdowns in just two seasons. On top of simply putting up numbers, Strong's prowess forced opposing defenses to put a major focus on him, opening up other receivers.
Who might replace him? Gary Chambers Sr. - At 6'4 206, Chambers has the size to replace Strong and will be given a good shot at becoming the Sun Devils' go-to possession receiver. He is going to have to really step up his production, but his combination of size and athleticism will give him a great chance to do that.
Cal - WR Chris Harper
The Bears took a blow when junior Harper declared early for the draft a bit unexpectedly. Harper was one of the best receivers in Cal's Bear Raid fleet and even if he didn't have as good of a junior year as he did sophomore year, he will be sorely missed.
Who might replace him? Trevor Davis Sr. - The Bears have plenty of great receivers with Kenny Lawler, Bryce Treggs and Stephen Anderson coming back, but they will need another speedy receiver to step in for Harper and senior burner Davis could be that guy. Davis is most known as a standout return man, but he also had nearly 400 yards receiving and caught five touchdowns in 2014.
Colorado - G Daniel Munyer
A starter for almost all of his career, Munyer has been a long mainstay up front for the Buffs while being an All-Pac-12 selection. He has been one of the Buffs' best players seemingly forever at this point.
Who might replace him? Shane Callahan Jr. The massive (6'6 300) Auburn transfer has had Buff fans excited with his SEC background, but he only saw reserve time in 2014. With Munyer and fellow starting guard Kaiwi Crabb graduating, expect Callahan to step into a starting role.
Oregon - QB Marcus Mariota
Mariota probably has the biggest shoes to ever be filled at Oregon. On the surface, it looks almost impossible.
Who might replace him? Jeff Lockie Jr. - It is going to be a wide open battle to replace Mariota, especially considering that the Ducks might bring in a big time transfer or true freshman, but Lockie is the one with the most experience going in. Lockie has stepped in for Mariota in stints and looked like a speedy player, but will have quite a battle in front of him this spring to succeed the Heisman winner.
Oregon State - QB Sean Mannion
The record-breaking passer is finally off to the NFL after a seemingly neverending college career and the Beavers are going to look a lot different in 2015. The big-armed signal caller has helped a struggling Beaver program stay afloat and with no clear successor, it is going to be tough to replace him.
Who might replace him? Luke Del Rio So. - Jack's son served as Mannion's backup in 2014 and saw a little bit of time in 2014. The race should be wide open between Del Rio and some other players, but he should have a leg up going into spring with his experience.
Stanford - T Andrus Peat
The Cardinal lose a handful of very valuable players, but none as good as Peat who is likely to be a Top 15 pick in the 2015 draft after declaring early. Losing Peat will be especially difficult because of the rest of the former highly-touted recruits who will return as starters on the Cardinal offensive line underwhelmed in 2014.
Who might replace him? Casey Tucker So. - The former five-star recruit looks like he could be the next All-American at tackle for the Cardinal, but he is young, seeing just reserve time in 2014. Tucker has all of the tools to become a star and I think will start at the tackle spot opposite Kyle Murphy, exactly which side that will be though, I am not sure.
UCLA - QB Brett Hundley
The Brett Hundley era at UCLA is finally at an end. Hundley never quite reached Mariota-level status, but he was the Pac-12's second-best quarterback for about three years and everything he did will be nearly impossible to immediately replace.
Who might replace him? Jerry Neuheisel Jr. - There is a lot of buzz about five-star true freshman Joshua Rosen coming in and winning the job in spring, but Neuheisel is the proven back-up who won at game against Texas in Texas when Hundley went down in 2014. Rosen might take the job from Neuheisel in the long run, but I am giving Jerry the inside track for now.
USC - DE Leonard Williams
Williams is a guaranteed Top Five pick and a one-man wrecking crew up front for the Trojans this year. You simply do not replace 6'5 295-pound defensive linemen who can play any position up front, stuff the run and rush the passer.
Who might replace him? Claude Pelon Sr. - A junior college transfer, the 6'4 295 Florida native has a lot of similarities with Williams even if his production was dwarfed by the All-American in 2014. He probably cannot fill Williams' massive shadow, but he could easily turn into an All-Pac-12 player if he grow with an expanded role.
Utah - DE Nate Orchard
The nation's sack leader was impossible to block off of the edge and it really bolstered Utah's pass defense. His presence on the edge will be sorely missed by Utah in 2015.
Who might replace him? Hunter Dimick Jr. - Dimick quietly had a good season across from Orchard with 2.5 tackles-for-loss and two sacks. He could become a standout up front if he can develop without Orchard around commanding blockers.
Washington - DT Danny Shelton
The 340-pound Shelton was an All-American that could go as high as the Top 10 in this year's draft as an athletic plugger in the middle. It is going to be very hard for the Huskies to replace the backbone of their defense.
Who might replace him? Elijah Qualls So. - Qualls was a back-up to Shelton and impressed in limited time. He will get a chance to shine next year with Shelton graduating.
Washington State - WR Vince Mayle
Mayle had the best stats of any receiver in the Pac-12 this year as a nearly unstoppable target in Mike Leach's offense. The Cougars have a few good receivers, but none as big or fast or productive as Mayle.
Who might replace him? River Cracraft Jr. - Cracraft has been huge for the Cougars, especially in 2014, but he is going to have to turn it up a notch to fulfill the void left by Mayle.