Ceanothus spinosus is a large treelike shrub approaching 6 metres (20 ft) in maximum height.

[1] The thick, firm evergreen leaves are hairless, oval, and up to an inch wide, with smooth margins.

[1] The stipules (small leaf-like structures at the base of the leaf stem) are thin and fall off early.

[1] The shrub blooms in inflorescences up to 15 centimeters long filled with clusters of white to pale blue flowers.

[1] The fruit is a smooth, round capsule about half a centimeter wide containing three lobes.