In 1972, Yosemite National Park established a wilderness fire zone in which lightning fires were allowed to run their courses under prescribed conditions, which was later expanded in 1973. From 1973 to 2011, there have been 157 fires in the basin. Fire severity data were collected on all 28 of those fires that were larger than 40 ha. The main effects were significant for unchanged severity and low severity, and the interaction between return interval class and burning index class was significant for high severity. The factors that were associated with reburn severity worked in combination with each factor influencing some aspect of severity. Managers and scientists can use this information to better understand the role that fire plays in these ecosystems and how to best manage this dynamic ecological process.