The San Francisco 49ers roster has seen a massive transition since head coach Kyle Shanahan and general manager John Lynch took it over from the previous regime last year.

Shanahan was asked on Tuesday how he would assess the work he and Lynch have done to transform the 49ers to match their vision for the roster.

"I've been happy with it," Shanahan said. "I thought we had a lot of work to do when we got here. Just looking at our roster, where we're at over a year time span, we've got one guy on our offense who has started before we got here in Joe Staley. I want to say we've got three guys left for the entire offense with (Garrett) Celek, Joe Staley, (Joshua) Garnett, and (Aaron) Burbridge. So that would be four guys.

"And that takes a lot of work. Not just draft picks but free agents, and not the big ones everyone sees in just the first couple of days, but just the depth and everything that we've had to do. It's been a lot of turnover. You don't realize until you get out there and you start looking at the board.

"On defense, there's been a lot also. Not quite as much just because most of the draft picks were there the few years before we got here. But it's totally different.

"There's a ton of turnover with everybody. And it's just nice going through this last year, you go out the first day, and everyone's practicing the right way, right away. You don't have to sit in here and show a bunch of clips and try to teach guys the standard. It's their standard now, and they've owned up to that. Those guys know how to set the way and guys just follow."

One of the players who is benefiting from having some experience under his belt is quarterback Jimmy Garoppolo. He joined the 49ers via a trade at mid-season last year and was forced to play catch up before (and while) starting the team's final five games.

"Everyone knows the crash course that Jimmy got last year," Shanahan said. "It's been nice to just slow it down and teach him some of the verbiage and the whys instead of just, 'Hey, memorize this by Sunday.' It's been nice for him to know why, and be able to relax, and talk through that stuff."