Biennials (or short-lived monocarpic perennials), 60-200 cm; taprooted. Stems several, erect to spreading, thinly arachnoid, soon glabrous; branches ± fleshy, usually much branched proximally, spreading to ascending. Leaves: blades ± elliptic, 30-75 × 10-20 cm, shallowly to deeply pinnatifid, lobes oblong to ovate, unlobed or with several prominent secondary lobes or large teeth, obtuse to acute, main spines 2-7 mm, abaxial gray arachnoid-tomentose, adaxial faces thinly arachnoid, glabrate; basal often present at flowering, spiny winged-petiolate; principal cauline sessile, bases clasping with broad, spiny-margined auricles, reduced distally, spinier than proximal; distal much reduced, spines 7-20 mm. Heads several-many, in congested corymbiform arrays. Peduncles 0-7 cm. Involucres ovoid to hemispheric or campanulate, 1.5-3 × 1.5-5 cm, sparsely to densely arachnoid, finely short-ciliate. Phyllaries in ca. 6 series, dark green or brown or with stramineous margins and a darker central zone, imbricate, linear-lanceolate (outer) to linear (inner), abaxial faces without glutinous ridge; outer and mid bodies appressed, spiny-ciliate, apices long-spreading to ascending long-acuminate, spines straight, stout, 5-15 mm; apices of inner straight or twisted, long, entire, flat or spine-tipped. Corollas dark reddish purple, 17-24 mm, tubes 8-11 mm, throats 3.5-6 mm, lobes 5-7 mm; style tips 3-4 mm. Cypselae dark brown, 4-5 mm, apical collars narrow; pappi 15 mm. 2n = 32.
Flowering spring-summer (May-Sep). Headlands, ravines, seeps near coast, sometimes on serpentine; of conservation concern; 0-100 m; Calif.
Cirsium andrewsii occurs along the coast of north-central California from San Mateo to Marin counties. It reportedly hybridizes with C. quercetorum (F. Petrak 1917; J. T. Howell 1960b).