Anticlea elegans

Anticlea elegans, formerly "Zigadenus elegans", is also known as mountain deathcamas, elegant camas or "alkali grass". It is not a grass (though its leaves are grass-like), but belongs to the trillium family, Melanthiaceae.
It has white lily-like flowers and two-pronged, greenish-yellow glands on each petal (the shape of which can help in distinguishing it from other members of the genus). It is widely distributed throughout North America and occurs in many habitats. Plants on the western side of the continent tend to be smaller in size than their eastern counterparts, but have more densely clustered flowers. The plant is extremely poisonous.
Meriwether Lewis, while on the course of his expedition in 1806, collected a specimen near the Blackfoot River.