Richard E. Lingenfelter, Steamboats on the Colorado River, 1852-1916, University of Arizona Press, Tucson, 1978, p.167 Richard E. Lingenfelter, Steamboats on the Colorado River, 1852-1916, University of Arizona Press, Tucson, 1978 , p.12 Gridiron lay along the east bank of the river 47 miles below what is now the Sonora/Mexico—Arizona/U.S. border. [