 Boise National Forest is a <unk> protected area covering 2 @,@ 203 @,@ 703 acres ( 8 @,@ 918 @.@ 07 km2 ) of the U.S. state of Idaho as part of the national forest system . <unk> on July 1 , 1908 from part of Sawtooth National Forest , it is managed by the U.S. Forest Service as four units : the Cascade , Emmett , Lowman , and Mountain Home ranger districts . 
