That pest is the Canadian Thistle.
It's identified as a "noxious weed" here in Colorado... and noxious is an excellent word to describe it... before you even realize what is happening, it can spread and take over a whole pasture!
I'm trying to get them all pulled (or chopped off) before the flowers to go seed. With the kid's help we are making good progress... there is only one not-too-big sized patch of them left on the property. (They had been growing in the low spots... the bottom of the gully, the dry lake bed, etc.)
This pile in the driveway is only the tip of the iceberg in terms of what we've pulled and chopped... We've got about twice a much still down in the gully waiting to be hauled up.
Except for these thistles (which are almost gone), the pastures are just beautiful right now... filled with wildflowers. M even found one today that smelled like cherry lifesavers. (He said it tasted like a cherry lifesaver too, and then I reminded him not to eat plants that he doesn't know... for sure... are food!)
Oh... the rain has stopped... time to head back outside and pull a few more of these miserable, stickery, things!