[2] Ceanothus crassifolius typically occurs in coastal and montane California chaparral habitat associations.

Common flora associates are Toyon (Heteromeles arbutifolia) and Hollyleaf cherry (Prunus ilicifolia).

[2] Ceanothus crassifolius is an erect, spreading shrub which can exceed 3 metres (9.8 ft) in height.

The small evergreen leaves have widely spaced teeth along the edges and the undersides are lighter in color and coated with hairs.

The inflorescences are borne on short stalks less than three centimeters long and are small and rounded with tiny white flowers.