Regional patterns of atmospheric nitrogen deposition (N_dep) are often estimated using direct measurements from large-scale monitoring networks and atmospheric chemistry models. However, in the western U.S., complex topography and weather patterns lead to heterogeneous deposition patterns that are difficult to predict. Additionally, δ¹⁵N values of deposition may inform sources of N. This study aimed to understand N_dep patterns in mountainous ecosystems and how isotope values, lichens and throughfall deposition can be used to determine N_dep sources and patterns in the Greater Yellowstone Ecosystem (GYE). In addition, we measured C:N ratios in lichens as an indicator of lichen physiological condition and ecosystem response to N_dep. We established ion exchange resin collectors and collected two lichen species (Letharia vulpina and Usnea lapponica) at 15 sites at four transects across the GYE. Mean summer N_dep measured by bulk collectors at each site ranged from 0.26 kg ha^-1 to 1.66 kg ha^-1. In remote areas, N_dep was higher than expected based on other studies in the area. The δ¹⁵N values of lichens were typically -15.3 to -10‰ suggesting agriculture as a primary emission source of deposition. C:N ratios for L. vulpina in this study ranged from 29.4 to 48.7, while for U. lapponica, C:N ratios ranged from 22.7 to 39.2 where lower C:N ratios indicate more N_dep. Overall, this study suggested that while regional patterns of N_dep can be estimated with modeling and large monitoring networks, N_dep also varies on small spatial scales that are more difficult to measure and lichen %N, δ¹⁵N and C:N ratios can provide information about N_dep sources and patterns in complex terrain.