On about May 18, 1961, Karl Hauswirth, the petitioner, was engaged in placing timbers or "ribs" in large structural steel forms, which were to be used in the spillway of the dam. Hauswirth was lifting the timbers, which weighed approximately fifty to sixty pounds, and holding them in place while one Francis Gameinhardt "spiked" or nailed the struts to hold the timbers in place. While so engaged Hauswirth claimed he felt a pain run through his back and right leg and immediately complained of it to Gameinhardt. Although continually complaining the remainder of that day and the next day, which was Friday, he remained at his job. After work on Friday petitioner accompanied a group of other workers in a car trip to Mesa, Arizona, in order that he might spend the weekend with his family. During the course of the automobile ride the pain in his back and leg intensified to extreme discomfort and when his associates returned to his home to pick him up the following Sunday afternoon to drive back to work he was unable to return with them due to his condition.