McMahon will be making his first career appearance on the Major League roster and will wear uniform No. 1. He has played 108 Minor League games this season across Double-A and Triple-A and has combined to bat .354 (152-for-429) with 71 runs scored, 37 doubles, three triples, 19 home runs, 82 RBI, 37 walks, 82 strikeouts and 11 stolen bases
A versatile infielder, McMahon has made 49 starts at first base, 32 starts at second base and 24 starts at third base this season. He won Player of the Week honors once with Double-A Hartford, and twice with Albuquerque. He was named Eastern League Player of the Month for April with Hartford and Pacific Coast League Player of the Month for June with Albuquerque.
In his Minor League career, McMahon has batted .297 (620-for-2091) with 340 runs, 171 doubles, 20 triples, 78 home runs, 386 RBI, 223 walks, 598 strikeouts and 40 stolen bases in 558 games across five levels of play.
He appeared in the 2017 Futures Game in Miami and went 0-for-1 with one walk as a defensive replacement at first base.
The Yorba Linda, Calif., native was originally selected by Colorado in the second round of the 2013 First-Year Player Draft out of Mater Dei High School in Santa Ana, Calif.
Tapia has batted .287 (35-for-122) with 22 runs, eight doubles, two triples, two home runs, 10 RBI and five stolen bases in 48 games across four stints on the Rockies active roster this season. He made his Major League debut for the Rockies on Sept. 2, 2016 vs. Arizona and has hit .281 (45-for-160) with 26 runs, eight doubles, two triples, two home runs, 13 RBI and eight stolen bases across 70 career games.
Additionally, Minor League left-handed pitcher Sam Moll was designated for assignment.