Stems (3-)4-10 × (2.5-)3-6.5 cm; ribs 13; areoles 12-16(-20) mm apart along ribs; areolar glands absent. Spines 12-20 per areole, tan to pale gray, pinkish, or yellowish brown (rarely dull white), usually tipped paler ('frosted') gray or blue-gray; radial spines 11-17 per areole; abaxial (shortest) radial spine 8-13 × 0.31-0.55 mm; adaxial and lateral (longest) radial spines (11-)14-21 mm; central spines (0-)1(-4) per areole, abaxial central spine usually straight, rarely porrect, 11-18.5 mm (absent in some populations); adaxial central spines erect and loosely appressed against radial spines, 12-25 × 0.4-0.5 mm. Flowers 2.3-2.6 × 2.4-3.1 cm; inner tepals white or creamy white, sometimes with midstripes or faint midlines of pale green, greenish tan, dull pinkish brown, or olive-gray, 1-2 cm × 1.5-4.8 mm; stigma lobes green or yellow-green. Fruits indehiscent or disintegrating irregularly, coffin-shaped, ± 10 × 6-10 mm. 2n = 22.

Flowering Feb-Mar; fruiting May-Jul. Chihuahuan desert scrub, low hills, gravelly bajadas, with sparse grasses and creosote bushes or in dense scrub with Texas false-agave, lechuguilla, and silverleaf, diverse substrates including limestone, tuff, and gypsum; 500-1000(-1400) m; Tex.

Echinomastus warnockii is very difficult to distinguish from E. intertextus var. dasyacanthus, except that the former has green stigma lobes and indehiscent fruits. Flowers of E. warnockii taper to their bases, unlike the broad-based flowers of E. intertextus. The photograph accompanying L. D. Benson´s original diagnosis of E. warnockii portrayed the relatively distinctive E. mariposensis instead, resulting in persistent confusion.

Echinomastus warnockii almost certainly occurs in Mexico but no specimens were seen in herbaria of Mexico or the United States.