Let's make a correction here, though it's one the average radio listener probably wouldn't have known. KDFC is located at 90.3 mHz and is licensed to San Francisco. KDFL, which simulcasts the programming of KDFC, is licensed to Livermore and is located at 89.9 mHz. My guess? Unless KDFC's main San Francisco transmitter is also down, there is a broken link between KDFC and KDFL. I'll let those who more than I do (if they choose) say what kind of link that most likely is.
Also, both stations are owned by the University of Southern California (USC, the owners of KUSC in Los Angeles) so any inquiries should go there.