Subshrubs. Stems erect, 400–700 mm, minutely hirtellous to hirsutulous with slightly deflexed, eglandular hairs. Leaves cauline, relatively even-sized; petiole absent; blade elliptic or oblong-elliptic to elliptic-lanceolate or elliptic-oblanceolate, (10–)20–55 × 4–17 mm, margins entire, serrulate, or mucronulate, plane or revolute, apex obtuse or rounded to acute, surfaces glabrous. Pedicels 5–12 mm in fruit. Flowers 2 per node, chasmogamous. Calyces not inflated in fruit, 20–30 mm, glabrous except for lobe apices, tube slightly dilated distally, lobes subequal, apex acute. Corollas pale yellow or nearly white to pale orange or light yellow-orange, not spotted or striped, palate ridges yellow to golden yellow, tube-throat 35–45 mm, limb 30–45 mm diam., bilabiate, lobes each apically incised 1/4–1/2 length, appearing 2-lobed. Anthers included, glabrous. Styles sparsely minutely glandular. Stigmas included, lobes equal. Capsules 15–25 mm. 2n = 20.
Phenology: Flowering Apr–Jun.
Habitat: Rock walls, dry rocky soils.
Elevation: 100–1600 m.
Diplacus grandiflorus (central Sierran) and D. linearis (coastal) are remarkably similar; it seems likely that they are vicariants. Leaves of D. linearis are narrower, and the nodes tend to be considerably more crowded. Corollas of D. linearis have narrower limbs, and both pairs of anthers and the stigma are at the same level and relatively deeply included. In D. grandiflorus, the anther pairs are separated, and the stigma is above the distal anther pair at or near the throat opening.