The fourth of a 10-part series that looks at where Pac-10 teams are strongest and weakest as they begin spring practices.

California

Strong: Offensive line

Why it's a strength: There isn't an area of the 2010 Bears that will blow you away, but the offensive line welcomes back five guys who've started at least seven games, as well as a couple of quality backups, though it was a hit when veteran guard Mark Boskovich opted to graduate instead of use his final year of eligibility. Donovan Edwards (seven starts) is the most likely candidate to fill a void at one of the tackle spots. The health of talented guard Matt Summers-Gavin is an issue after a shoulder injury and concussion limited him to eight starts in 2009. As a group, the Bears were better run-blockers (third in the Pac-10 in rushing) than pass-blockers (31 sacks surrendered) in 2010. The latter often improves with experience and continuity. If the unit stays healthy, it could be one of the stronger crews in the conference.

Weak: Secondary

Why it's a weakness: The Bears must replace two starters, including two-time first-team All-Pac-10 cornerback Syd'Quan Thompson, and experienced backup safety Marcus Ezeff from a crew that ranked ninth in the conference in pass defense (267 yards per game) and seventh in pass efficiency defense -- and was a huge disappointment in 2009. There are some interesting possibilities at safety, where Sean Cattouse, Chris Moncrease, Chris Conte and Vachel Samuels will compete (and touted incoming freshman Keenan Allen, though primarily a receiver, might be in the mix, too). Cornerback, however, is a question. Darian Hagan fell out of favor as a junior, while Bryant Nnabuife and Josh Hill often were picked on opposite Thompson. Samuels might be an option at corner. Opponents completed nearly 64 percent of their passes against the Bears in 2009 and threw 20 TD passes, which ranked seventh in the conference.