Stems erect to reclining, not rooting nodally, hirsute or sometimes pilose or glabrous, base not bulbous. Roots never tuberous. Basal leaf blades broadly ovate to semicircular or reniform in outline, 3-parted or -foliolate, 1.5-5.3 × 2.2-8 cm, segments usually again 1(-2)×-lobed, ultimate segments oblong or elliptic to lanceolate or oblanceolate, margins dentate (sometimes dentate-lobulate or entire), apex acute to rounded-obtuse. Flowers: receptacle glabrous; sepals reflexed 2-3 mm above base, 4-7(-9) × 2-4 mm, hirsute; petals 5-14, yellow, 5-13 × 1.5-8 mm. Heads of achenes hemispheric, 3-7 × 5-9 mm; achenes 2.6-3.6(-4.8) × 1.8-3(-3.2) mm, glabrous, rarely hispid, margin forming narrow rib 0.1-0.2 mm wide; beak persistent, lanceolate to lance-subulate, straight or curved, 0.4-2.2 mm.

The seeds of Ranunculus occidentalis were eaten by some Californian Indians. D. E. Moerman (1986) identified this taxon as an Aleut poison: juice of the flowers could be slipped into food to poison the person who ate it.