Summary: For millennia, forest ecosystems in California have been shaped by fire from both natural processes and Indigenous land management, but the notion of climatic variation as a primary controller of the pre-colonial landscape remains pervasive. Understanding the relative influence of climate and Indigenous burning on the fire regime is key because contemporary forest policy and management are informed by historical baselines. Our research on this topic was conducted with members of the Karuk and Yurok Tribes, USGS scientists, and USFS scientists. Our findings show that a fire regime consisting of tribal burning practices and lightning ignitions was associated with long-term stability of forest biomass. Before Euro-American colonization, the long-term median forest biomass was approximately half of contemporary values. Indigenous depopulation and 20th-century fire suppression likely allowed biomass to increase, culminating in the current landscape: a closed Douglas fir–dominant forest unlike any seen in the preceding 3,000 years. This is consistent with pre-contact forest conditions being influenced by Indigenous land management and suggest large-scale interventions could be needed to return to historic forest biomass levels.