prostratus forms as a mat, has a generally unfolded leaf, and produces fruit with erect horns.

[3][6] Ceanothus prostratus grows in the understory of mixed conifer forests, from foothills to subalpine areas.

It also inhabits open flats and ridges in areas of low chaparral[6] as well as dry interior forest ecosystems.

This subgenus likely began diversifying at the beginning of the Pliocene roughly 6 million years ago, when cool, dry conditions combined with the uplift of the Coast Ranges to create new and diverse habitats.

The closest relatives of C. prostratus within the subgenus Cerastes are Ceanothus pinetorum and C. purpureus, based on a phylogeny produced in a 2011 paper.

[9] Ceanothus prostratus is one of many plants in the region that colonize logged areas, forming brushfields in the wake of timber harvests when more light reaches the ground.