Calochortus nuttallii is a species of flowering plant in the lily family, Liliaceae. It is commonly called the Sego Lily or Mariposa Lily. The plant is native to western North America, ranging from British Columbia to California and east to Montana and Wyoming. It is a herbaceous perennial plant that grows from a bulb and produces one to several erect stems, each up to 60 cm tall, bearing one to several flowers.