Fox, who played four positions with the Cubs this past season, batted .259 with 11 homers and 44 RBIs in 82 games and had 17 homers at Triple-A Iowa. Miles, who signed a two-year deal with the Cubs prior to the 2009 season, hit a career-low .185 while struggling with injuries, coming off a .317 season with St. Louis in '08. The A's also received cash considerations in the deal.
"It's a real good trade for everyone," Cubs general manager Jim Hendry said. "Jake will help the A's, hopefully Aaron will get back on track. It gives us three good young players and a power arm with a chance to make the club in Gray."
With Miles and Fox in the fold, the A's have more infield insurance, which is key considering that veteran third baseman Eric Chavez's health is a big question mark and Adam Kennedy could leave Oakland via free agency. The A's also signed third baseman Dallas McPherson this offseason, presumably to compete for the job at the hot corner.
Miles, 32, has played the majority of his big league games at second base but also started 115 games at shortstop. He will be making a homecoming of sorts, having graduated from Antioch (Calif.) High School, not far from Oakland.
Gray went 0-1 with a 3.76 ERA in 24 appearances covering four stints with Oakland in 2009, registering 16 saves in 37 appearances for Triple-A Sacramento.
Morla, 21, went 1-7 with a 4.86 ERA in 17 appearances for Class A Vancouver, 12 as a starter. The 6-foot-4, 200-pound right-hander is 7-15 with a 4.52 ERA in 48 appearances (36 starts) in three Minor League seasons.
Spencer, 23, was acquired by the A's in the 2008 trade that sent pitcher Joe Blanton to the Phillies. The 6-foot-5, 240-pound infielder/outfielder combined to hit .289 with 34 doubles, 19 home runs and 91 RBI between Class A Stockton and Double-A Midland last season.
John Schlegel is a national reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.