On Tue, 25 Jun 2013 15:42:03 +0000, Kay Lancaster wrote:

it is indeed a member of the mustard family...
4 separate sepals, 4 separate petals, 6 stamens
(often 2 short and 4 long) and a two-chambered ovary.
http://waynesword.palomar.edu/images/silique1.gif

Thanks for the helpful identification.

What I see clearly (and which matches the wild mustard ID) a
- 4 unveined yellow petals (aka sepals)
- 6 long things (aka stamens), 2 of which are shorter
- One thing in the middle (aka pistil)
http://www3.picturepush.com/photo/a/...g/13410171.jpg

And, now I recognize there a
- Lots of seed pods (aka immature siliques)
http://www3.picturepush.com/photo/a/...g/13410166.jpg

And:
- Lobate leaves which radiate out of the ground:
http://www1.picturepush.com/photo/a/...g/13410179.jpg

Plus:
- Hairy stems
http://www1.picturepush.com/photo/a/...g/13410169.jpg

And, most unusual, that it "takes over (my) wasteland":
http://www2.picturepush.com/photo/a/...g/13410185.jpg

One remaining question:
Q: How does it know "my" yard is currently a wasteland?

PS: The sprinkler system is partially broken; there's an electrical
problem in some of the zones in that they don't work electrically
but they work mechanically if I turn them on at the box in the ground.