I went to the Fountain Lake on Tuesday evening, hoping to get a shot of the Fountain at sunset. I got a shot, but the sunset was unremarkable. I waited around until the 7:00pm Fountain and got a very different shot entirely.
I took this photo of these trees roughly 10 minutes after sunset.
This is the 7:00pm Fountain, taken over an hour after sunset.
As I was walking around the Fountain Lake to return to my car, I noticed another good spot from which to take a Fountain photo in the future. I took a test shot and was surprised at the result. This is a 20 second exposure, taken at f/4.5, ISO 640. I was amazed at the color of the sky. It was quite dark by this time. I could make out a glow in the sky to the left, but it was quite a lot darker. I could also see the saguaros and their shadows on the water, but none of the detail on their grassy island.