Birds of Prey in The Valley

While normally associated with shopping malls and suburban sprawl, The Valley outside L.A. also has some nice wildlife habitat. Earlier this month we went in search of birds at the Sepulvida Basin Wildlife Reserve. We saw ducks with bright blue beaks, coot chicks, cormorants, and all other kinds of stuff. The real highlight was this bird, calmly observing the scene. We came back a half hour later and it was still there. We think it might be an American kestrel in an uncommon ghostly white and gray plumage. But it looked a little bigger than kestrels are supposed to, and I don't see any vertical bars under the eyes, so another guess would be Northern Harrier. What do you think?