Sourgrass, Bermuda buttercup.
An invader from Africa. It can be found on the lower reaches of most trails and beside roads and fire-roads. It can cover hillsides. There’s a large patch under burnt oak trees on Jesusita trail just above the last ranch.
Over the summer the plant vanishes. It reappears in early November after the first significant rain perhaps. First bloom observed mid-November. Finished in May.
At night, the flowers furl up into little cylinders which unfurl again with the day.