Calling All Amateur Botanists

I found this wildflower growing on the bank of the creek running through my backyard: 

It's got small, star-shaped white flowers with a cluster of short yellow stalks in the center; almost like a narcissus, only with very different stem and leaf structure. (See, it's got one stem, with all the leaves coming off of it, and two flowers at the top).

Its leaves are kind of weird-looking, too --- they're much larger than the flowers, longer than they are wide, with edges that I'm not sure whether to call serrated, because the "points" are so rounded. 

Here's a close-up of the flower: this picture isn't as clear as the others, because I had to move closer to the plant to take it, and the flower is growing out of a fairly steep creek bank. Thus I was in an unstable position when I took it, and wasn't really able to steady the camera. 


(I notice, though, that while the flower in that picture might be out of focus, the thorns on the stem show up beautifully. Auto-focus can be a very strange thing.)


So, does anyone know what this is?