I live between San Jose and San Francisco and (sampling bias I mainly ride my bike during the day) I've seen foxes a couple of times in the suburbs (once about two miles outside Cupertino and once in Portola Valley where people like Larry Ellison have an estate) over twenty years, and probably a coyote at least once a month and a bobcat maybe twice a year and three mountain lions over the same time period, a fox is rare to see in the day but they are nocturnal so mostly not active during the day. The average person is more likely to encounter fox scat without knowing that's what it is.