Perennials, 100-300 cm; caudices and taproots, spreading by creeping roots. Stems 1-several, erect or ascending to lax and hanging, glabrous or thinly tomentose; branches 0-few, ascending. Leaves: blades elliptic, 30-90+ × 10-40 cm, 1-2 times pinnately lobed, lobes linear to ovate, strongly undulate, main spines slender, 5-15 mm, faces often glaucous, glabrous or thinly tomentose and soon glabrescent; basal present at flowering, petiolate or winged-petiolate; proximal cauline winged-petiolate; mid sessile, much reduced, less deeply lobed, bases clasping, short-decurrent 0-2 cm; distal linear or lanceolate, bractlike, very spiny. Heads few-many, erect or nodding in clusters at tips of distal branches in paniculiform arrays, not closely subtended by clustered leafy bracts. Peduncles 0.5-6 cm. Involucres hemispheric, 1.4-2 × 1-2 cm, phyllary margins thinly tomentose or glabrate. Phyllaries in 5-8 series, strongly imbricate, (green, drying green or light brown), ovate to lance-oblong, abaxial faces with or without poorly developed glutinous ridge; outer and mid bases appressed, margins entire, not scabridulous-ciliolate, apices spreading or reflexed, green to brownish, lance-ovate, elongate, flattened, spines slender, 3-25 mm; apices of inner straight, entire. Corollas dull white to pink or purple, 16-20 mm, tubes 7-8.5 mm, throats 4-6.5 mm, lobes 4.5-6 mm; style tips 2.5 mm. Cypselae gray or brown, 3.7-4.5 mm, apical collars not differentiated; pappi 10-15 mm. 2n = 34. Flowering spring-summer (May-Sep). Hanging gardens, seeps, stream banks; 1000-1500 m; Ariz., Utah. Cirsium rydbergii is endemic to the Colorado Plateau of northern Arizona and southeastern Utah.