Coastal Deerweed (Acmispon glaber var. glaber)
https://www.inaturalist.org/observations/25363153 by @bonnienickel
Short-wing Deerweed (Acmispon glaber var. brevialatus) https://www.inaturalist.org/observations/25762684 by @ingorenner

Deerweed (Acmispon glaber) is abundant in San Diego County, found from the coast to the desert, and includes two varieties, coastal deerweed (A. glaber var. glaber) and short-wing deerweed (A. glaber var. brevialatus). Coastal deerweed (also known as California broom) and short-wing deerweed are almost equally represented in our county. Of 433 voucher specimens at SDNHM and 338 iNaturalist observations verified by Jon Rebman, 55% are of A. g. var. glaber and 45% are of A. g. var. brevialatus which means you can’t count on relative abundance to help you determine which variety of deerweed you find.

As the common name implies, coastal deerweed is the variety found on the immediate coast. Once you are just a few miles inland, both varieties are found all the way to the mountains. In the desert and desert transition, short-wing deerweed is the likely variety. Due to the extensive overlap in all but the extreme margins of the county, distribution is not of much help in determining the variety in most of our area.

The best way to separate the two is to examine the flowers, which are usually present March through August. Like other members of the Fabaceae, the flowers of Acmispon have 5 petals which are arranged and named differently from most other families. The uppermost petal is called the banner, 2 lateral petals are called the wings, and 2 bottom petals are fused and called the keel. In coastal deerweed (A. g. var. glaber), the wings are about equal in length to the keel. In short-wing deerweed (A. g. var. brevialatus), as you might expect, the wings are shorter than the keel.

If you post an observation of deerweed from San Diego County on iNaturalist, be sure to include a photo of a flower with enough resolution to show the wings and the keel.