Sometimes called "ant-money," the seeds of the legume (pea and bean family) Psoralea lanceolata are commonly collected by harvester ants. The Psoralea plant is usually just referred to as tumbleweed, a term for any plant whose dry branches and foliage separate from the root and blow away. This helps the plant's seeds scatter widely.
Learn more about Colorado's plants at the University of Colorado Herbarium.