From that article:
Some ash collected in residential areas after the October fires registered a pH of 12.7, a level more caustic than ammonia and nearly as caustic as lye.
To clarify: there is no way to measure the pH of something except as it exists in aqueous solution, and by definition the aqueous solution of wood ash, given time to leach, is basically lye. All wood ash is highly alkaline. Historically this feature was a driving force for the production of potassium hydroxide, before the onset of industrial production techniques. There is nothing particularly different about the ash from California wildfires compared to any other wood ash.
I have explained how and why wood ash is alkaline, given one of its most common water-soluble ingredients is potassium hydroxide. The effects on garden soil would be completely dependent on the quantity and amount of time it has to wash out. A little ash mixed into the soil is no big deal; a lot of ash will tend to have more dramatic, longer-lasting effects. Compost mixed in with the ash will tend to attenuate its alkalinity as compost is somewhat acidic. There's no need to panic about wood ash having a high pH. We knew that before we heard the latest measurements.
