Pre-1800, about 1.8 million ha burned each year in CA:
https://www.sierraforestlegacy.org/Resources/Conservation/Fi...
> Approximately 1.8 million ha burned annually in California prehistorically (pre 1800). Our estimate of prehistoric annual area burned in California is 88% of the total annual wildfire area in the entire US during a decade (1994–2004) characterized as ‘‘extreme’’ regarding wildfires. The idea that US wildfire area of approximately two million ha annually is extreme is certainly a 20th or 21st century perspective. Skies were likely smoky much of the summer and fall in California during the prehistoric period.
See also: https://royalsocietypublishing.org/doi/full/10.1098/rstb.201...
> Many consider wildfire as an accelerating problem [...] however, important exceptions aside, the quantitative evidence available does not support these perceived overall trends.