McMahon will be on the Rockies' Opening Day roster, Nick Groke of The Denver Post reports.
It's something of a surprise move, as reports suggested after the Rockies signed Carlos Gonzalez that McMahon would have to start the season in Triple-A. The 23-year-old infielder has impressed this spring, hitting .328/.375/.537 in 29 games. He dominated the Triple-A level last year, hitting .374/.411/.612 in 70 games for Albuquerque, so he had little left to prove in the minors. McMahon's exact role for the Rockies is unclear -- he can fill in at first, second and third base. First base may be his spot against righties, while the bench may be his home against lefties. He could return good value for his draft price, as anyone with a decent bat who plays half of his games at Coors Field is a potentially significant fantasy asset.