Envelope reads "Hetch Hetchy Calaveras tunnel explosion 6/30." Photograph shows five men seated on what appears to be a pile of lumber. The to men on the right sit with legs and arms crossed. To their left two men have their arms around eachothers' shoulders. The man on the left sits with his elbows on his knees and his hat in his hand. Two of the men wear overalls, and the other three wear pants and shirts. For more information about the Calaveras Tunnel and the Hetch Hetchy project see h99.1.470.