Galls of Artemisia tridentata Nutt. of Utah County were collected and described in detail. Of the ten galls collected, seven were caused by members of the Itonididae, two by members of the Trypetidae, and one by a member of the Curculionidae. Of the seven Itonid galls, six were caused by species of Diarthronomyia, and one by a species of Rhopalomyia. Two of the galls were caused by new species of Diarthronomyia. Three genera of the Scelionidae (Hymenoptera) and four genera of the Chalcidoidea (Hymenoptera) were also reared from the galls. A key to the ten galls was constructed, but does not necessarily include all the galls of big sagebrush of Utah County. To the writer's knowledce this is a first report of Eutreta diana O. S. (U. S. Geol. Sur. of Terr., 1877) in Utah. The position of the galls in their relationships as to complexity and specialization and possible origin has been pointed out.