Perennials, 10-30 cm (not or scarcely cespitose, not matted); proximal indument thinning with age, grayish, arachnoid-sericeous to thinly lanuginose. Stems mostly 5-15+, ascending to erect. Leaves mostly cauline, 2-5 cm; largest blades ± elliptic, ± plane, 1-pinnately lobed; lobes mostly 2-5 pairs, remote, ± plane. Heads mostly 1-3 per stem. Peduncles ascending to erect, 2-5 cm. Involucres ± obconic. Phyllaries: longest (10-)12-15 mm; outer closely lanuginose, not stipitate-glandular, apices erect, ± rigid. Corollas 7-9 mm. Cypselae 7-9 mm (eglandular); pappi: longest scales 3.5-5 mm.
Flowering Jun-Aug. Rocky or gravelly serpentine slopes, scree, talus, openings in or above conifer forests; of conservation concern; (900-)1200-2200 m; Wash.
Chaenactis thompsonii appears to be sister to C. evermannii; it is known from the mountains of central and northwestern Washington. The similar habits of C. thompsonii and C. ramosa (= C. douglasii var. douglasii) appear to result from convergent evolution in the distinctive habitat of their type localities (Wenatchee Mountains), not from a close genetic relationship as suggested by Cronquist.