Biennials or monocarpic perennials, acaulescent or caulescent, 5-110 cm; taproots stout. Stems erect, stout, fleshy, leafy, simple or distally branched, villous or tomentose with long, septate trichomes; branches usually short, stout, ascending. Leaves: blades oblong-elliptic to oblanceolate, 15-30+ × 3-7 cm, usually shallowly to deeply pinnatifid, lobes ovate to broadly triangular, spreading, usually separated by broad U-shaped sinuses, spinose-dentate or coarsely lobed, main spines 2-5(-8) mm, slender, abaxial faces villous with septate trichomes, at least along veins, sometimes thinly arachnoid, adaxial villous with septate trichomes; basal often present at flowering, spiny winged-petiolate; principal cauline winged-petiolate or sessile, not much reduced distally; distal reduced, similar to proximal, crowded around heads. Heads 1-5(-9), borne singly or crowded in corymbiform arrays at tips of main stems, often closely subtended and overtopped by 1-several distal leaves. Peduncles 0-5(-10) cm, leafy-bracted. Involucres broadly ovoid to hemispheric, 3.5-5 × 3.5-5 cm (appearing much wider and ± campanulate in pressed specimens), loosely arachnoid on phyllary margins or glabrate. Phyllaries in 4-6 series, strongly imbricate, ovate or broadly lanceolate (outer) to lance-linear (inner), abaxial faces with ± narrow glutinous ridge; outer and mid appressed, spines erect to ascending, 2-3 mm; apices of mid and inner narrowed and scabrid-denticulate, innermost spineless, with expanded, flexuous, erose-denticulate tips. Corollas purple (white), 30-48 mm, tubes 17-30 mm, throats 6.5-11 mm, lobes 5-7 mm; style tips 5-7 mm. Cypselae stramineous to light brown, 3.5-5.5 mm, apical collar yellow, narrow; pappi 30-42 mm.
Cirsium drummondii is widely distributed across Canada from the Northwest Territories to British Columbia and Ontario. The name C. drummondii has been misapplied to a wide range of plants across the western United States that are now treated as one or another variety of the polymorphic C. scariosum. The only documented modern occurrences of C. drummondii in the United States are in the Black Hills of South Dakota and adjacent Wyoming. Specimens collected by Hall and Harbour (342) are the only ones of C. drummondii known from Colorado. Somewhat similar plants from northern Nevada are treated here as C. scariosum var. toiyabense. During Pleistocene glaciations the ancestors of C. drummondii undoubtedly occupied a more southerly distribution and very likely came into direct contact with populations of C. scariosum. The observed similarities between C. drummondii and C. scariosum var. toiyabense are probably a relict of that ancient contact.