Oakland also officially announced the signing of free agent outfielder Gabe Gross to a one-year contract -- initially reported by MLB.com on Sunday -- and claimed infielder Steve Tolleson off waivers from Minnesota.
Rosales, 26, essentially represents the final piece to the A's offseason puzzle as a young utility infielder. It became obvious he was the key player in the trade when Oakland immediately designated Taveras -- along with left-handed pitcher Dana Eveland and eventually Gregorio Petit -- for assignment.
"He's exactly what we needed for a utility infielder," A's assistant general manager David Forst said of Rosales. "He plays some outfield too, and he's a relatively young guy with not that much Major League service time who we feel could potentially be here for a while.
"Our scouts have seen a lot of him over the past few years, and every single one of them just loves the way he plays the game and really likes his versatility."
Rosales, who will most likely be used to spell Cliff Pennington at shortstop this season, played all four infield positions while batting .213 with four home runs and 19 RBIs in 87 games with Cincinnati last season.
On the flip side, the 33-year-old Miles -- acquired by the A's along with Jake Fox and $1 million from the Cubs on Dec. 3 -- has more experience at shortstop but is primarily a second baseman and comes with a heftier price tag. He hit .185 in 74 games for Chicago last year and will make $2.7 million this season.
Meanwhile, the A's have a 10-day window to take care of Taveras, who departed Cincinnati after one unsuccessful season as the Reds' leadoff hitter. In 102 games, he hit .240 with a .275 on-base percentage and 25 steals.
Taveras is due $4 million in 2010 -- a fairly large price tag the A's are hoping to unload soon.
"We're making contact with teams to see if there's someone interested," Forst said. "We've got 10 days to figure that out."
If the A's can't unload the 28-year-old Taveras, they will have essentially paid $1.3 million for Rosales' rights. But it's safe to say they are not in need of another outfielder, especially with the signing of Gross, who hit .227 with six homers and 36 RBIs in 282 at-bats last season for Tampa Bay. He can play all three outfield spots and figures to provide a left-handed hitting option off the bench while at the same time pushing aside any notion of a Johnny Damon reunion in Oakland.
"Gabe's always been a solid defender, a guy who hits right-handers well," Forst said. "We just felt like he was a good fit for the team, whether it's spotting some of our guys against tough righties or filling in at times since he can play both corner outfield positions. We've always liked the way he plays, and we feel he's a good fit for the team the way it's constituted right now."
The move begs the question of where Gross' presence leaves a handful of other outfield options, most notably Travis Buck and Eric Patterson -- the latter who, according to Forst, seems to have the edge in competing with Gross as the team's fourth outfielder.
At the same time, Forst made sure to note Buck "has every opportunity to play well and make this team, but he needs to earn his way here."
Joining Buck -- and several others -- in the hunt for a spot on the Opening Day roster will be 26-year-old Tolleson, who combined for a .266 average, eight home runs and 40 RBIs in 130 games for Double-A New Britain and Triple-A Rochester in the Twins' farm system last year.
"He's another guy our scouts have liked since seeing him play in the Arizona Fall League in 2008," Forst said. "He's somewhat similar to Rosales, just a couple years behind. He can play a number of positions and helps add to the depth."
Both Rosales and Tolleson have options left, which affords the team plenty of flexibility as it enters the season with question marks surrounding another utility infielder named Eric Chavez.
More than enough depth will be on display at Spring Training in just a few weeks' time, but Forst said Monday's hoopla of transactions doesn't necessarily mean the club is quite done wheeling and dealing.
"We've got three players on designation, so we need to make moves and figure out how to resolve those situations," he said. "We never close the door on anything. I think we're very happy with the roster as it looks right now, but we'll certainly sign guys right up until the first day of Spring Training and even, like last year, into Spring Training."
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.