Calochortus dunnii is a rare species of flowering plant in the lily family known by the common name Dunn's Mariposa lily. It is native to Baja California and San Diego County in California, where it is known from only a few occurrences in the chaparral and forests of the local mountain ranges. It is a perennial herb growing a slender, branching stem up to 60 centimeters tall. The waxy, channeled basal leaf is 10 to 20 centimeters long and withers at flowering. The flower cluster bears 2 to 6 erect bell-shaped flowers. Each flower has three sepals and three white or pinkish petals. The petals are up to 3 centimeters long and spotted with red and yellow near the bases, where there are patches of yellow hairs. The fruit is a narrow, angled capsule 2 to 3 centimeters long. The main threat to the existence of this rare species is collecting by admirers of the attractive flowers.