It was found in Northern Colorado and grew in clusters. They were small purple flowers with four (?) petals. The following is a photo of the plant I'm referring to. Thanks for your help.
http://www.flickr.com/photos/marisarenee/7165967134/in/photostream
meanolmaw
Favorite Answer
http://www.colostate.edu/Dept/CoopExt/Adams/weed/damesrocket.htm
they start easily from seed.... if you see it again when the seeds have formed, take some home with you..... in your area it should not be too 'invasive'.... but you can keep it contained by removing seed heads in your garden....
stone
Looks like Dame's rocket, Hesperis matronalis.
sciencegravy
Looks like Dame's Rocket.