"Oakland's migration of All-Star starters continued Thursday, when the team traded Gio Gonzalez.

The left-hander, among the most coveted trade targets this offseason, went to Washington in exchange for right-handers A.J. Cole and Brad Peacock, left-hander Tom Milone and catcher Derek Norris. Washington also will receive Class A right-hander Robert Gilliam.

"It's still surprising to me, even after all the speculation," Gonzalez said by phone Thursday evening. "When they called to let me know, I was like, 'Man, I grew up in Oakland. I matured there.' There are so many things I can credit to Oakland; the list is too long to fit in my house.

"It's a heartbreak to leave, but it's on to a new chapter."

The trade has not been officially announced while the teams await the players' physicals; Gonzalez's will be conducted today in Washington.

"This was the guy we wanted," one Washington source said, speaking of Gonzalez, who was an All-Star in 2011 when he went 16-12 with a 3.12 ERA. Gonzalez is 26 years old, and though he is arbitration-eligible for the first time this winter, he is under team control for four more years.

The A's received four of Washington's top 10 prospects, according to some rankings, including the team's consensus No. 3 prospect, Cole, and No. 4, Peacock. Cole, 19, is probably three years away from the big leagues, but Peacock, 23, is likely to be in the mix for a spot in the rotation this spring.

Norris, 22, who hit .210 with 20 homers at Double-A last season, has been ranked as high as the team's second-best prospect in previous years, and Milone, 24, is considered a savvy pitcher with a strong changeup.

"I don't know if Oakland could have done better," one major-league scout said. "They got the right set of names. Quality and depth."

The A's, however, lose their top starter on the heels of dealing No. 2 starter Trevor Cahill to Arizona on Dec. 9. The club is in rebuilding mode while awaiting word on potential approval for a new stadium."