This stuff is all over Coyote Hills park in Fremont, CA ... I THINK it's poison hemlok, but I really can't be sure ...
SOLVED: Poison hemlock, anise, or yarrow?
The apparent absence of bracts (leaves) immediately under the umbel (flower cluster) suggest that it is not poison hemlock (Conium maculatum), but some closer photos would help, as well as some photos taken when it is in the growing season to show the leaves, stems, etc.. It's not yarrow either. Your plant is an umbellifer.
Perhaps wild fennel then? I'll try to get more pictures of this next time I'm out there...
Looks like Foeniculum vulgare,
Fennel for me too, though close-ups needed to be 100% certain.