Thanks to the Aggies for the picture above.
Those pretty yellow wildflowers are an example of Western Bitterweed.
Bitterweed can, and will take over a pasture, especially in times of drought. It is toxic to livestock - particularly sheep - and even a small amount can turn a cow's milk into something that tastes too nasty to believe. As a kid, I learned to never be the first to taste a new bottle of milk.
It is probably close to sixty years since I last tasted Bitterweed infused milk, and I don't know what made me think of it today, but just the thought of it makes my mouth feel nasty.