49ers build around Jimmy Garoppolo in 4-round mock NFL Draft

Round 1, Pick No. 12 Overall: 49ers select offensive tackle Rashawn Slater, Northwestern

There’s a lot hinging on what the Niners do with eight-time Pro Bowl left tackle Trent Williams, who’ll be a free agent this offseason and could easily command a new deal worth $20 million annually.

If Williams walks, it’s a problem. San Francisco doesn’t have a starting-caliber option to fill his void currently on the roster.

Even if Williams stays, though, the 49ers would be smart to continue investing in the offensive line, which Football Outsiders ranked ninth in pass protection last year but 22nd in run blocking.

While Oregon’s Penei Sewell is the bona fide top lineman in this year’s class, Northwestern offensive tackle Rashawn Slater isn’t too far behind and could be pegged as the next lineman selected in what’s considered to be a deep O-line class. Slater moves well, as evidenced by his outstanding 4.88 40-yard time at his pro day:

But the fit goes beyond just being mobile.

Slater is a versatile piece. Should Williams be re-signed, the Niners could plug Slater in at right guard as a plug-and-play starter, thereby reverting offensive lineman Daniel Brunskill back to being an uber-reserve type, which is what San Francisco needs of him.

Yet if Williams departs in free agency, Slater is good enough a prospect to be in line to secure the starting left tackle spot, too, using his combination of speed, size and strength to solidify a long-term role as a key bookend.

Hopefully giving Jimmy Garoppolo the protection he needs against his blind side.