Clark reported the news of the deal first last week on his Twitter account.
The 26-year-old Clark produced a .282/.359/.494 line over parts of five Minor League seasons with 102 home runs as a first baseman in the Padres' farm system.
Clark, the son of former Major League pitcher Terry Clark, was a 12th-round pick in the 2008 First-Year Player Draft out of Louisiana State University.
Clark spent the last two seasons with Triple-A Tucson, where he hit 23 home runs in 2011 and 22 home runs last season.
Clark, who had been left off the 40-man roster after the 2011 and 2012 seasons, was impressive during Spring Training a year ago. He hit .419 with four home runs and 13 RBIs in 43 at-bats.
But Clark was blocked by Yonder Alonso, whom the team obtained in December 2011 from the Reds in a five-player deal that sent Mat Latos to Cincinnati. Alonso, 25, hit .273 with 39 doubles and 62 RBIs in his first full Major League season.