East end of a cross levee on Robert's Island. Clay soil.
Tall grasses, growing along a fence line on MetroLink rail right of way, San Dimas Canyon Road, just S of Arrow Highway. Inflorescences distinctly red. Coin used for scale is a US quarter dollar (¢25 piece), 24.26 mm, 0.955 inch in diameter. Last photo taken some steps away from point of collection, so ignore the different looking soil in the background.
I think it is bumelia, but would like a second opinion.
Sorghum bicolor
http://biology.burke.washington.edu/herbarium/imagecollection.php?Genus=Sorghum&Species=bicolor
If this is wrong, thenI am stumped as to what it might be.