Try your county's Extension Service office for info.

Locate that office with this interactive map:

http://npic.orst.edu/pest/co untyext.htm

Did you ever get an answer? It is Yellow Star Thistle. May also be heard as Malta star thistle. It is a very invasive and noxious weed. It will take over native grasses and wild flowers. Can be toxic to horses if they don’t have any other forage.

Hello, This is Malta Star Thistle. I have been dealing with it for a few years now. I do not use herbicides so have been pulling it up and disposing of it in trash bags. I have less and less each year. There are chemicals to control it also. Its best to jump right on it so it cannot spread. I is a noxious weed as the previous poster said. One of the worst I have dealt with. Look online for more information.