The California spotted owl (CSO) is a subspecies of conservation concern that resides at the center of forest planning efforts in California. CSO populations have been monitored in local areas with mark-recapture based demographic studies for decades, but the distribution, trends, and status of CSO outside of these areas is less well understood. Therefore, we developed and, in 2021, implemented a bioacoustic monitoring program that spanned most suitable habitat in the Sierra Nevada to estimate trends and understand patterns in site occupancy. We deployed autonomous recording units (ARUs) at over 1,700 sites for approximately 5 weeks each, yielding approximately 1 million hours of passively recorded avian vocalization data. Audio data was scanned using a novel machine-learning algorithm (BirdNET) trained to detect five different CSO vocalizations. Here, we present estimates of CSO site occupancy for the Sierra Nevada bioregion in 2021 and, by scaling occupancy estimates to densities within demographic study areas, provide the first estimate of population size for CSO in this part of their range. Our study demonstrates the feasibility of monitoring rare, vocally active species over regional scales with bioacoustics – providing not just an understanding of population trends but also locational information central to forest planning efforts.