Stems erect, spheric to ovoid-cylindric, 30-90(-250) × 30-60(-100) cm; ribs (15-)21-32, shallowly notched immediately above each areole. Spines 6-10 per areole, reddish, reddish gray, or horn colored, all robust and rigid, more than 1 mm diam.; central spine 1, curved (hooked only on relatively young plants), annulate, thick, adaxially flat, 55-95(-130) × 2.5-4 mm. Flowers reddish outside, brilliant red inside, 6-7.5 × 5-7.5 cm; inner tepals brilliant red [yellow]; stigma lobes brilliant red. Fruits ± readily dehiscent through basal pore, bright yellow, 25-50 × 25-35 mm, leathery or fleshy, locule dry, hollow except for seeds. Seeds 2 mm, pitted. 2n = 22.
Flowering summer-early fall. Hillsides, wash margins, alluvial fans, mesas, or flats, gravelly rocky or sandy soils, rocky slopes and adjacent bajadas, Sonoran desert scrub, igneous substrates; 0-1200 m; Ariz.; Mexico (Sonora).
Ferocactus emoryi has a confused taxonomic history. The name is based on Echinocactus emoryi, which was published twice by Engelmann, each involving a different species. Engelmann´s first use of E. emoryi [in W. H. Emory]---applied to a population of Ferocactus wislizeni in eastern Arizona---is rejected as provisional and therefore invalid. However, Engelmann´s second use of E. emoryi was a valid publication, and it unambigously pertains to the species in southwestern Arizona that Britton and Rose unncecessarily re-named as Ferocactus covillei.