This paper summarizes results from an intensive study of 28 firepits from the NAN Ranch Ruin, a prehistoric Mimbres site, in order to understand differences in prehistoric use of indoor and outdoor firepits. This study reveals that indoor and outdoor firepits were used for cooking and processing food, although outdoor firepits were more frequently used for processing wild plants with seed remains. Small animals were cooked in both indoor and outdoor firepit areas, and bone evidence suggests that they may have been spitted and roasted. Hardwood fuel sources, which will produce a longer burning fire with less smoke, were more frequently chosen for indoor fires, and softwoods were more frequently chosen for outdoor fires.