This link says that South Mountain Park is open from 5am to 11pm
http://phoenix.gov/PRL/reserve.html

Here is a copy of the web page I made on Nov 4, 2009. The only change I made was to put a <a name="south_mountain_hours"> tag so you can jump to the hours for South Mountain Park and don't have to search for them.

This link that says that the ramadas that you can reserve in South Mountain Park are open from 8am to 10pm. It doesn't mention that the South Moutain Park hours for other uses are 5am to 11pm.
http://phoenix.gov/PARKS/hikesoth.html
click on
Ramada map and information
and this url pops up with the park hours
ftp://www.phoenix.gov/pub/PARKS/smtnram2.pdf
Here is my copy of the pdf file which I made on Nov 4, 2009.

While the hours of South Mountain Park are 5 a.m. to 11 p.m. many of the signs at the park either do not list the hours, or the signs list incorrect hours. Two of the signs I photo graphed listed hours of 5 a.m to 7 p.m. and 5 a.m. to 7:30 a.m.

When I was arrested the cop lied to me and told me the park was only open until 7:00 p.m.

False Arrest in South Mountain Park