Wall Barley, Mäusegerste, Hordeum murinum.
One of many wild grasses I pulled last week around Pasadena. Took pictures later, while waiting for a meeting to begin, hence the background.
This grass grows like a weed or an invasive species, cropping up anywhere it can.
I found it under a tree placed near a sidewalk.
Collection No. 13231: A. Williams, F. Leist, R. Brostrom, S. Tsiu, W. Dreskin; flowering, 1 plant, roadside