To answer Out on the prairie's question about my previous post, I went back and looked at the other photos from that day. Here's one of a different bloom that includes a bit more of the foliage. I also found a good image at this link. It does not resemble thistle the way prickly poppy does. I know prickly poppies also have some pretty good stickers (they are named appropriately). You can see that this foliage is darker, and more smooth and "friendly" than that of its prickly cousin.
Matilija poppies are also quite large—they grow up to eight feet tall. The ones in my photographs were only about waist- or chest-high. Now, for those of you who are wondering what a prickly poppy looks like, CalPhotos has some good examples of a variety that's native to California.
Thanks for asking—I always like learning new things about flowers!