Green-spored Parasol

I'd say it's C. molybdites for a couple of reasons: first the location on grass and in an urban environment, secondly as a mushroom of the southwest, third due to the substrate (it's found growing on well-kept irrigated lawn, i.e. grass) and lastly because of the brown warts (little specs on the cap) on a white cap.
Compare with this one from Glendale: http://www.projectnoah.org/spottings/739...
Don't think about eating it unless you're just asking for a couple of horrible days and nights!!