I also concur with Dave in LA's identification as Descurainia sophia. The photos on this web page, particularly the close-up of the flowers,...
It's not pineapple weed. The flowers are not as close together as that, and there is no smell in the crushed flowers. If it's an umbillifer, any...
Here are more photos. I crushed the flowers, but no pineapple smell. The flowers are very interesting, though my lens could not capture...
I live in Boulder Colorado, and this plant has popped up in my yard in a few areas. It is now about 18 inches tall and at the top has a few...