The genus Acronicta looks good to me. There are a lot of BG images there that look like a possible match...among them A. grisea and A. radcliffei...although neither of those have any current BG records from CA, which gives me a bit of pause for those candidates.

Both of those species have record of occurrence to central California. See MPG for example.
http://mothphotographersgroup.msstate.edu/species.php?hodges=9212

Thanks, Dick, for your interest and suggestions here. I got a chance to research the ID for this moth more thoroughly this evening...and I'm now convinced it's Acronicta as you suggest.

As for species...you're correct in pointing out that both A. grisea (BG, MPG, PNW Moths) and A. radcliffei (BG, MPG, PNW Moths) are known from CA...and there were willows nearby this photo locale, which are among the host plants for both those species. Nevertheless, neither seemed quite right to me after scrutinizing fine details of their markings, and reading about details of their habitats and CA ranges on the (excellent!!) PNW Moths web pages. Moreover, the California Moth Database records for A. grisea and A. radcliffei were mainly from forested areas of the Sierra Nevada and far northern CA, which are fairly different habitats from the arid mixed blue oak/chaparral/grassland habitat where this moth was found.

Upon further perusal of the PNW Moths Acronicta page I briefly thought that A. dactylina and A. impleta looked promising...until I read and saw that they lacked the basal dash apparent in my moth here, and again their habitat/ranges didn't seem right.

Finally, I noticed that A. marmorata (BG, MPG, PNW Moths) was an excellent visual match in all aspects, had an oak woodland habitat, and had numerous records from the CA coast ranges. In fact, there are more CA records for A. marmorata on the California Moths Database than for any other species of Acronicta, and in particular, there is a record from Del Puerto Canyon...where this photo was taken. Also, the PNW Moths page mentions A. marmorata feeds on deciduous oaks, and the dominant oak in the area, California blue oak (Quercus douglasii), is deciduous.

So my best shot at the ID here is A. marmorata.

This is a tough group at the species level. Bet the species we discuss are closely related. Good work.

I just lined up (in consecutive browser window tabs) "zoomed-in" right wing images from the PNW Moths web pages for a number of Acronicta species, and then cycled through the tabs carefully cross-referencing those images with the right wing of my post here. I looked at species grisea, radcliffei, dactylina, impleta, impressa, and marmorata...those seeming to be the best candidates culled from smaller-sized images.

As Merrill Petersen states in his PNW Moths descriptions, grisea and radcliffei have an overall smoother, more uniform "speckling" than the other three, with marmorata having the most pronounced, high-constrast mottling (or "marbling" á la its epithet)...and the other two species being intermediate in the degree of contrasting speckling/mottling.

When all those images are lined up and cycled through, it becomes quite clear that my image agrees best with marmorata. That, together with the more mesic habitats and largely disjoint ranges described for the other 4 species on the PNW Moths page, and the Cal. Moth Database record of marmorata from Del Puerto Cyn convince me that A. marmorata is the best choice. Thanks for setting me on the right track here, Dick.