I found several of these on or around Lemonadeberry (Rhus integrifolia) and suspected that it might be the caterpillar of the Channel Islands endemic Lophocampa indistincta (despite there being no photos or description of the larvae available on the net), so I sent the photo to Jerry Powell who replied:

"yes, the image certainly must be Lophocampoa indistincta, as there are no
other Lophocampa recorded on Catalina. Its overall color is a brighter
yellow than in my image of a caterpillar from Santa Cruz Island, where I
found them on Vaccinium. If you collected larvae, you can expect adult
emergence in August or Sept. This species escaped notice on Catalina for a
century because lepidopterists worked there mostly in spring and missed
the Aug- Sept. flight."

This photo adds the caterpillar to BugGuide (and the greater internet in general).