The pretty pink corolla of mimulus bigelovii
consists of five partly fused petals, two at the top, two at the sides and one beneath; the color becomes darker towards the center, with a prominent yellow patch at the base of the lowest lobe, edged by darker purple bands. Modified sepals beneath the flower form a hairy, ribbed calyx.
Leaves have an opposite arrangement along the purplish stems. Stems, leaves and calyces are densely soft-hairy. In drier desert environments the plant grows just an inch or two off the ground, and the leaves are small and purplish, but moister locations see the flower stalks reach heights of 6 inches or more, while the leaves are greener and larger.