The black powder and dynamite used in the routine State work in Yosemite Valley were kept in the "Tool House" before John Degnan built this stone magazine in the 1890's. In addition to thick stone walls, the powder house also had six inches of sand in the ceiling as protection from fire.

Later, the powder house was converted into a jail - a very poor one. In 1915, two young car thieves escaped by digging away the mortar between the rocks with a leg they had twisted off the rickety steel frame cot. The pair claimed the task was so easy that they waited until after breakfast to perform their escape. Patrol rangers recaptured them, and shackled them by leg irons to the corners. Following this incident, horseshoes were imbedded in the floor to provide a chain base of greater security. Occasionally, the powder house - jail also served as a morgue.