There seems to a strong basis for the suspicion that some of the fires were started by arsonists.
There was a coordinated arson attack last month in which four homes under construction were destroyed and two others damaged. One of several banners found at the sites in north San Diego read:
"Development destruction. Stop raping nature. The ELFs are angry."
ELF stands for Earth Liberation Front
a lunatic criminal environmentalist group that admits dozens of acts of arson and vandalism, including a $50 million fire that destroyed a residential development in San Diego in early August.