We conducted the first assessment of small mammal diversity for three unusually low-elevation stands of Rocky Mountain juniper, known locally as swamp cedars, in White Pine County, Nevada, between 24 May and 1 June 2016. These small patches of woodland add considerable habitat diversity to the expansive low-elevation shrublands in Spring Valley and White River Valley. Spring Valley stands supported unique small mammal communities, most notably through the occurrence of pinyon mice (Peromyscus truei). In contrast, no pinyon mice were detected in the much sparser and smaller White River Valley stand. Instead, it harbored typical Great Basin shrubland mammals. Our results suggest the novel communities in Spring Valley swamp cedar habitats may be threatened by planned groundwater removal.