It looks like a dandelion on steroids–a big, mean, nasty dandelion. The flowers are sunny little composites that dry into carefree puffs. But it grows to be six feet tall… and the entire plant is prickly. This is bristly ox-tongue, or Helminthotheca echioides.
One of the most unique aspects of bristly ox-tongue are the pale blister-like bumps on its leaves. I have seen a huge variation in size; often it is only ankle-high, but sometimes (even in the same general area as the smaller versions) the stalks can grow as tall as my shoulder.
This species is a late bloomer, with flowers beginning in June but continuing in places all the way until December. It is native to the Mediterranean but isn’t highly invasive. You will usually see it growing it seasonally wet or damp soils. It has no medicinal or traditional uses that I know of.
Flowers Of Marin 