These can only be arson. It's so sad to see the fires in the Valley and North San Diego County destroying so many homes, property, horses and pets. Very upsetting. It's strange that the first of the fires started around Ventura County and quickly spread east while the Santa Ana winds were blowing from the east to west.
I live in Murrieta (Inland) and we had a small 300 acre fire that started on Wednesday in a hilly remote area, mostly ranches. Fortunately Cal Fire brought in one of their 727's within an hour and started dropping fire retardant. Fortunately they had the fire under control by Friday with minimal structure loss and no loss of life .
Considering the area, there is no reasonable explanation of how it started, other than arson. On Thursday night a vigilant diner in a restaurant in Anaheim Hills (site of a previous fire a few months ago that destroyed 100+ homes) spotted a small fire on a hillside out the window and enlisted another man to check it out while calling 911. They spotted the arsonist, chased him thru the canyon and cornered him until police arrived.
Thankfully the winds are finally receding and the firefighters will finally be able to get the fires under control. God Bless 'em!