Link goes to tonight's scoreboard, which lists Jang as the starting pitcher.
Jang pitched for the rookie level AZL Angels in 2009, leading that staff with 6 wins and 82.1 innings while putting up a 3.83 ERA. He throws primarily in the high 80's.
Chaffee will likely start as well, since the Quakes just sent AA Arkansas two starters (Manuel Flores and Jayson Miller), but it remains unclear where he slots in the rotation. Chaffee's plus stuff helped him post the best batting average against of all Midwest League starters in '09, but he has historically struggled with his command.