Wildfire Suppression Difficulty Index (terrestrial) (SDIt) is a quantitative rating of relative difficulty in performing fire control work. In its original formulation for use in Spain, SDI included aerial resource use, however for development and application in the United States we removed the aerial resource component due to a lack of consistent data. We note this distinction of  terrestrial only calculations with the inclusion of  t  in the acronym. SDIt factors in topography, fuels, expected fire behavior under severe fire weather conditions, firefighter line production rates in various fuel types, and accessibility (distance from roads/trails) to assess relative suppression effort. For this dataset severe fire behavior is modeled with 15 mph up-slope winds and fully cured fuels. SDI has a continuous value distribution from 1-10. Here it is binned to six classes from lowest to highest difficulty.