Los Angeles has an abundance of starting pitchers, and Harang was left out of the rotation this season despite a steady track record. General manager Ned Colletti said the deal gives the Dodgers another backup at catcher behind starter A.J. Ellis.
The Rockies immediately designated Harang for assignment. They have 10 days to trade, release or send him outright to the minors.
Vice president of baseball operations Bill Geivett said Colorado will attempt to move Harang and get back something in return.
"With Aaron, we've always respected him and what he could do in the past. But we really have committed to five starters and we know he wants to start," Geivett explained. "We also have a group of younger pitchers in (Triple-A) Colorado Springs right now and we'd like to make sure that there is opportunity at some point in the season for them to come up and pitch on the big club.
"We know (the Dodgers) were talking to a number of clubs and I spoke with Aaron's agent. We'll begin those discussions now," he added.
Hernandez has a career average of .264 with 166 home runs, 751 RBIs and 1,335 hits during his 14-year career with Oakland, San Diego, Baltimore, Cincinnati and the Rockies. Colorado, which owed him $3.2 million, designated him for assignment on March 29.
The 36-year-old catcher was an All-Star in 2003 and averaged 118 games behind the plate from 2000-11. Among active players, only A.J. Pierzynski has caught more games and more innings than Hernandez, who has caught nearly 12,000 innings during his career.
Harang hadn't appeared in a game for the Dodgers this season. He was 10-10 with a 3.61 ERA in 31 starts last year. The right-hander is 105-104 with a 4.19 ERA in 11 seasons with Oakland, Cincinnati, San Diego and the Dodgers.
"He's been a very good pitcher at the big league level and a good starting pitcher. He's been a pro," Geivett said. "Those are things that everybody around the league that's seen him pitch or been around him knows."