Walden was born November 16, 1987, in Fort Worth, Texas, and graduated in 2005 from Mansfield High School. While playing for the amateur league team D-BAT Mustangs of Carrollton, Texas, he was teammates with future fellow MLB pitcher Clayton Kershaw. After attending Grayson County Community College, Walden was drafted in the 12th round of the 2006 draft by the Los Angeles Angels of Anaheim he did not sign until a year later in May 2007.

He was drafted by the Angels in the 12th round of the 2006 Major League Baseball Draft, and began his professional career the next season.

Walden pitched for the Orem Owlz in 2007, going 1–1 with a 3.08 ERA in 15 starts. In 64 ¹⁄₃ innings, he allowed 49 hits and three home runs while striking out 63 batters. Prior to the 2008 season, Baseball America named Walden the 81st best prospect in minor league baseball. He split that season between the Cedar Rapids Kernels (with whom he went 4–6 with a 2.18 ERA in 18 starts) and the Rancho Cucamonga Quakes (5–2, 4.04 ERA in nine starts), going a combined 9–8 with a 2.76 ERA in 27 starts. He pitched 156 ¹⁄₃ innings, allowing 122 hits and seven home runs while striking out 141 batters.

Before the 2009 season, Walden was named the 70th best prospect in baseball. He pitched for the Arkansas Travelers and went 1–5 with a 5.25 ERA in 13 starts that season. In 2010, he converted to relief pitching, spending 38 games with the Travelers and six games with the Salt Lake City Bees without making a start.

...
Wikipedia