Sorry for the long-delayed response, but it's likely most of the tornadoes in California were on the weak end of things, based primarily off of sheer probability plus the lack of favorable large-scale conditions (instability, dynamics, and so on) to support the stronger tornadoes. The terrain can muck things up a little bit -- albeit the extent to which that can occur may be the subject of some debate -- but generally, there likely wasn't enough energy or vertical wind shear (e.g. wind changing speed and direction with height, generally from S at the surface to W or NW not far aloft & increasing in magnitude) to support any of the massive tornadoes.

It's pretty rare for regions outside of tornado alley (give or take some areas north and south) & into the Ohio River valley to see anything stronger than an F3. It happens, sure, but the majority of those events occur where tornado frequencies are the greatest to begin with. It's interesting to note too that the U.S. hasn't seen an "official" F5 since the May 3, 1999 tornado that passed just south of Oklahoma City.