There are several species of the genus Acmispon, and they are difficult to distinguish. I’m taking a wild guess that this is the Acmispon glaber, otherwise known as Common Deerweed, California Broom or Western Birds-Foot Trefoil.
Found in dry areas of CA, it blooms from March to August. Its flowers are tiny, 7-11 mm, yellow and clustered together. They become reddish with age. The A. glaber food is consumed by hummingbirds, bees, butterfly and deer. In sufficient amount, it is a habitat and shelter for the world’s rarest butterfly, the Palos Verdes Blue, found only in southwest LA County. These A. glabers were found in Santa Cruz Mountains.