An analysis of 77,987 station-years of streamflow-gaging station data from 3,748 stations in the Rocky Mountains indicates that there is a latitude-dependent elevation limit to substantial rainfall-produced flooding. The elevation limit ranges from about 1,650 m in Montana to about 2,350 m in New Mexico. Above this elevation limit, large rainfall-produced floods occur very infrequently and maximum unit discharge is 1.7 m3/s/km2 or less. Below this elevation limit, large-magnitude flooding is more common and maximum unit discharge ranges from to 30 m3/s/km2 in Idaho and Montana to 59 m3/s/km2 in New Mexico. These results emphasize the critical need for additional research to increase our knowledge of floods, and have important implications in water-resources investigations in the Rocky Mountains.