In principle, genetic augmentations can rescue inbred populations from extinction vortices. In practice, genetic rescue is seldom used as a management tool due to uncertainty about risks and long-term benefits. We analyzed 34 whole genome sequences of North American red foxes to support planning for genetic augmentation of a small, isolated population of Sierra Nevada red foxes (Vulpes vulpes necator) in the vicinity of Lassen National Park, California. We found high levels of recent inbreeding in the Lassen population and elevated homozygosity of putative deleterious alleles, supporting inbreeding as a plausible factor influencing viability. We then evaluated the genomic suitability of candidate source populations by comparing the demographic histories and levels of deleterious variation across multiple North American red fox populations. Montane populations share a long-term history and became isolated from each other relatively recently, suggesting low risk of outbreeding depression. Different intensities of anthropogenic declines, however, have created tradeoffs in the potential and realized load of novel deleterious alleles that source populations may contribute to the Lassen population. Such tradeoffs may be particularly influential in genetic rescue of extremely small populations and thus bear careful consideration in source selection for the Lassen Sierra Nevada red fox.