We were alerted to its' presence by the beautiful song.

Bewick's Wren (Thryomanes bewickii) is a small, fast-moving songbird in the Wrens (Troglodytidae) family.
It has a long erect and upright tail, pale underside, and a long white eyebrow (bold white supercilium).
It actively forages by climbing and hopping about on trunks, branches and twigs of trees, probing into bark crevices or gleaning insects from the surface. It also feeds on the ground, flipping over leaves and probing among leaf litter. It feeds on a wide variety of insects, including beetles, ants, wasps, true bugs, caterpillars, grasshoppers, and many others. It also eats many spiders, and occasionally some berries or seeds.

Audubon Guide to North American Birds https://www.audubon.org/field-guide/bird/bewicks-wren

"Long-tailed, rather slender wren. Dark brown above and pale grayish below with whitish eyebrow. Slender bill is slightly decurved. Favors dry scrubby areas, thickets in open country, and open woodlands near rivers and streams. Also at home in gardens, residential areas, and parks in cities and suburbs. Song is variable, but usually includes high-pitched buzzes and musical trills."
E Bird: https://ebird.org/species/bewwre/

The Cornell Lab (Birds in U.S. and Canada) https://www.allaboutbirds.org/guide/Bewicks_Wren/

My favorite Bewick's Wren photo/observation: https://www.inaturalist.org/observations/190842946

Xeno-canto Bird songs, sound recordings, and species range map: https://xeno-canto.org/species/Thryomanes-bewickii

National Geographic Field Guide to the Birds of Western North America, ed. Jon L. Dunn, 2008, pp. 300-301.

Monterey Birds, Don Roberson, 2nd ed. 2002, sponsored by Monterey Peninsula Audubon Society, p. 360.

National Geographic Field Guide to the Birds of North America, ed. Jon L. Dunn, 7th ed., 2017, pp. 394-395.

Merlin Bird ID (great app available for Iphones) by The Cornell Lab (Bird ID help for 8,500+ species) https://merlin.allaboutbirds.org/

Comprehensive Feather I.D. tools and more: https://foundfeathers.org/resources/

Found Feathers (Worldwide): https://www.fws.gov/lab/featheratlas/idtool.php