Eaton signed a minor league contract with the organization June 9, where he was 3-3 with a 2.67 ERA in 12 games. The 33-year-old pitcher was released by the Orioles on June 6 after starting eight games and going 2-5 with an 8.56 ERA.
Chacin, one of the Rockies' top pitching prospects, was sent down a day after making his first major league start. He lasted 2 2-3 innings, giving up four runs and walking six.
He was 0-1 with a 5.87 ERA in five overall games for Colorado.
To make room for Eaton on the 40-man roster, the Rockies transferred left-hander Alan Embree to the 60-day disabled list.