Beetle biodiversity, particularly of leaf litter fauna, in the Sierran mixed-conifer ecosystem is poorly understood. This is a critical gap in our knowledge of this important group in one of the most heavily managed forest ecosystems in California. We used pitfall trapping to sample the litter beetles in a forest with a history of diverse management. We identified 287 species of beetles from our samples. Rarefaction curves and nonparametric richness extrapolations indicated that, despite intensive sampling, we undersampled total beetle richness by 32–63 species. We calculated alpha and beta diversity at two scales within our study area and found high heterogeneity between beetle assemblages at small spatial scales. A nonmetric multidimensional scaling ordination revealed a community that was not predictably structured and that showed only weak correlations with our measured habitat variables. These data show that Sierran mixed conifer forests harbor a diverse litter beetle fauna that is heterogeneous across small spatial scales. Managers should consider the impacts that forestry practices may have on this diverse leaf litter fauna and carefully consider results from experimental studies before applying stand-level treatments.