Several of the live oak trees in the older part of St. John’s Cemetery in San Mateo have branches on which grow bluish-gray foliose lichens with ruffled edges lined with black cilia. The thallus appears to be attached to the substrate mostly in the middle, leaving the edges curling up. On some, small round soralia could be seen (a soralium is where a lichen produces soredia, which are small bits of fungal hyphae and phtyobiont that can be released to produce a new lichen).
After consulting Stephen Sharnoff, A Field Guide to California Lichens (Yal Univ., 2014), I’d place these lichens in the genus Parmotrema; without doing any chemical tests, I’d guess P. arnoldii Powdered Ruffle Lichen, or P. perlatum Common Powder Ruffle.