I think it’s a milk thistle, from the white on the leaves. That’s not a US native, however, so if it’s not an imported species, it’s at least probably a close relative.
ETA: Wiki says milk thistles are used in herbal medicine, so perhaps it’s possible that some imports have “escaped” in California.
nothing to add, other than to say that there was a lot of those around my house growing up, and my brother and I used to enjoy grabbing the heads off those plants and throwing them at each other.
What “stinging toxins”? I’ve never heard that milk thistle (or other thistles, for that matter) have any deleterious properties associated with coming into contact with the plant apart from the unpleasantness of mechanical piercing of the skin, or maybe contact dermatitis in susceptible individuals. They don’t act like stinging nettles.
There may be some value in milk thistle preparations taken internally for signs/symptoms of liver toxicity, though a lot of the evidence is either anecdotal or comes from preliminary scientific studies.