In 1949, struggling with a heart condition, the 79-year-old Loper attempted another river run of the Colorado River through Grand Canyon. Launching July 7, 1949, Loper, Harris and six others attempted the run. Loper was rowing his self-built boat, The Grand Canyon, through 24½ Mile Rapid in the Marble Gorge of the Grand Canyon on July 8, 1949, when he became unresponsive and his boat flipped in the rapid. River historian Otis "Dock" Marston speculated Loper, with his perilous heart condition, was most likely dead before the boat flipped.Marston, Otis R., (2014). "From Powell To Power; A Recounting of the First One Hundred River Runners Through the Grand Canyon. Flagstaff, Arizona: Vishnu Temple Press, p. 454
