Trillium petiolatum Pursh
Collected along the Lolo Trail between Lolo Creek and Eldorado Creek near the mouth of Lunch Creek in Idaho Co., Idaho, on 15 Jun 1806. (Source)
It is a perennial, low, inconspicuous plant with 1 white flower on a short stalk that grows from the center of a whorl of 3 broad, ovate leaves at top of an otherwise leafless stem. The flower has a whorl of 3 leaves; petals purple, generally about the same length as sepals; sepals 2.5 to 6 cm. The leaves are long petiolate, rounded to obtuse, blade 8 to 13 cm, not mottle. It blooms very early in the spring in wet areas in the prairies and woodland edges of Western Oregon, Washington and Eastern Idaho.