Animal gut microbiome is often a key requirement for host nutrition, digestion, and immunity. Gut microbiomes can shift in relation to host geography and environmental factors. However, ecological drivers of microbiome community assembly across large geographic ranges have rarely been examined in invertebrates. Oreohelix strigosa (Rocky Mountainsnail) is a widespread land snail ranging across the mountainous western United States. O. strigosa is found in a variety of environments, including dry Southwestern habitats and the near-alpine of the Rocky Mountains. It is ideally suited for biogeography studies due to its broad distribution, low migration, and low likelihood of passive transport via other animals. This study aims to uncover large-scale geographic shifts in the composition of O. strigosa gut microbiomes by utilizing samples from across its native range. Additionally, we elucidate smaller-scale microbiome variation using samples collected only across the Colorado Front Range. Our results show that O. strigosa gut microbiome is variable across the broad geographic range. Within Coloradan samples, we investigated several possible ecological drivers of the geographic variation, including soil and vegetation composition, habitat complexity, habitat type, and human impact. We conclude that several small-scale environmental factors may be driving the changes in O. strigosa gut microbiome composition seen across large-scale geography. Uncovering large-scale shifts in the gut microbiome compositions will help form fundamental questions about the functional aspect of these qualitative changes. This knowledge will also help us better understand how microbial associations influence species survival in diverse environments and aid wildlife conservation efforts.