Carpenter Bees, Xylocopa

There are a few species of this large black bee Carpenter Bee that are native to California.
Mountain Carpenter Bee, Xylocopa tabaniformis orpifex
Valley Carpenter Bee, Xylocopa brasilianorum varipuncta
California Carpenter Bee, Xylocopa californica californica
the intermediate between californica and arizonica is Xylocopa californica diamesa,
Arizona Carpenter Bee, Xylocopoides californica arizonensis

Carpenter bees have certain tastes in wood and prefer good wood, not rotten wood for nesting material.  Xylocopa tabaniformis orpifex  is the most problematic for buildings and loves redwood or cedar posts (or trees) and will spend weeks digging a 1/2 by 4-6 inch hole into same for their nest site. The other species use a variety of woody material from Alder, Douglas Fir, Fruit trees, Cottonwood, Redwood, Cedar  Eucalyptus, Walnut, Yucca and other soft woody material. Xylocopoides californica arizonensis, likes desert plants like Agave, Cottonwood,(along washes) and Yucca.  Xylocopa californica diamesa, seems to prefer Yucca.

If you find these busy bees digging into your house, bug it to leave and plug the hole. That is usually enough to get it to move to your neighbors house. Barns build out of redwood or cedar have a tendency to be very holy here.