Fremont's star-lily
Toxicoscordion fremontii (formerly Zigadenus fremontii)
Melanthiaceae (formerly Liliaceae)

I'm not positive about this ID to species. It's apparently related to the soap plant.

ps 03/10/11 & edited 07/26/11 - I'm positive about this ID, because the stamens are less than 1/2 the perianth. I've also updated the names and links.