Call first.
By A Yahoo! Contributor, 9/4/11
Their website says to call first if it's raining to see if they're open, but you should call even if it's not raining. Their website says after September 1, they're open until 4. We arrived on a beautiful Saturday afternoon, September 3 at 12:45 and were told they were closed. I asked about the hours posted on their website and was told they, "extended summer hours for a few weeks," due to a heat advisory. Newsflash: This is Phoenix, it's hot here.
They didn't even have the courtesy to post a sign at the gate saying they weren't really open. There were two cars in the parking lot, so we proceeded to the cashier's window where a woman came out to close the shutter over the window and told us they were closed.