Pacific trillium is plant 20 to 40 cm tall. Leaves are verticillate. Unbranched stem bears only one flower. The flower is regular, with three petals, 25 to 50 mm in diameter, white, later pinking. Pacific trillium blossoms from late March to June. It grows in half-shade, in moist forests and wetlands, in altitude up to 2100 m. It ranges in southwest Canada, Washington, the Coast Ranges up to southern California, northeast Oregon, western Montana, around headwaters of the North Platte River, along Sweetwater River, and in the Rattlesnake Range of central Wyoming.
Rhizomes of Pacific trillium were used during childbirth (Tallbull 1993: 55).