What is the grassy ball in westerns?

Question:

What is the grassy ball in westerns?

You know in stereotypical old western scene when the gunfighters meet at high noon for a shoot out there is a driedout out grassy ball that rolls past. What is that ball called? I am writing a story and I can't discribe this thing.

Best Answer - Chosen by Asker: It's a tumbleweed. They are Russian Thistles that break off at ground level at the end of their growing season.