Common Linanthus? (Linanthus androsaceus)?
Or could this be the Small-Flowered Linanthus (L. parviflorus)? Probably not -- Lp is in the Serpentine Grassland, and this was near Escobar Gate -- but... We did not see into the flower, broken heart (La) or heart (Lp). It is hard to tell before the flowers open??