Ceanothus tomentosus is an erect shrub (occasionally tree-like) approaching 3 m in maximum height.

The evergreen leaves are alternately arranged, elliptic to oval in shape, dark green and with short hairs on the top and woolly on the undersides.

[3] The specific epithet tomentosus refers to the dense, interwoven trichomes on the plant.

[2] In Mexico, this species is found in the northwestern part of Baja California, from Tijuana to the southern end of the Sierra de San Pedro Martir.

[7] This plant primarily occurs on open sites on slopes, ridges, chaparral, and coniferous forest.