Plants perennial. Stems 5-8 dm, diffusely branched, often decumbent, copiously long-prickly. Leaf blades: surfaces sparingly long-prickly on veins; basal and proximal lobed nearly to midrib, lobe length often to 5 times width; distal not clasping. Inflorescences: buds ellipsoid-oblong, body 15-18 × 12-15 mm, prickly; sepal horns slender, terete, 12-15 mm, prickly at base. Flowers 7-10 cm broad; petals white; stamens 100 or more; filaments pale yellow; pistil 3-carpellate. Capsules narrowly ellipsoid-oblong, 35-45 × 10-14 mm (including stigma and excluding prickles), closely prickly, longest prickles 8-10 mm. Seeds ca. 2 mm.

Flowering spring; fruiting summer. Precipitous slopes; of conservation concern; 1000-2000 m; Ariz.

Argemone arizonica grows well in Grand Canyon National Park, especially along the Kaibab and Bright Angel trails.