Per Aaron Wilson, aka @ravensinsider:

The details are in on running back Marshawn Lynch's four-year, $31 million contract that beat the NFL deadline to use the franchise tag. The deal includes a $6 million signing bonus, according to a league source. The contract averages $7.5 million per year. It includes base salaries of $4 million in 2012 and $7 million in 2013 that are fully guaranteed for skill, injury and salary cap.

Lynch's base salary is $5 million in 2014, which is guaranteed for $ million for injury only if he's on the roster for the first game of the 2013 regular season, and $5.5 million in 2015. The deal includes a $500,000 roster bonus in 2014 where he's paid $31,250 for every game that he's active and a $2 million roster bonus in 2015. The annual salary cap figures are $5.5 million, $8.5 million, $7 million and $9 million.

To clean it up a bit - Marshawn Lynch received a 4 year, $31M contract with a $6M signing bonus.

His base salaries are as follows:

2012 - $4M
2013 - $7M
2014 - $5M
2015 - $5.5M

The Base Salaries in 2012 and 2013 are fully guaranteed.

The deal includes $500k in roster bonuses in 2014 and $2M in roster bonuses in 2015. (Basically those bonuses are divided by every game played in those years).

Here are his Cap Numbers for the next 4 years (Cap Number = base salary + (signing bonus/total number of years) +other bonuses for that year):

2012 - $5.5M
2013 - $8.5M
2014 - $7.0M (if he plays all 16 games)
2015 - $9.0M (if he plays all 16 games) (If he played 8 games in 2015 his cap number would be $8.0M)

There is a clause where the salary is guaranteed for injury only in 2014 and 2015 if he is on the roster for the first game of 2013. Seahawks can still cut him for skill or cap reasons so I don't know how much teeth that clause really has. I wouldn't count on the 2015 season playing out as is, and am not that confident in 2014 -but we will see. Congrats Marshawn! Well earned.