Originally Posted by pls8xx
Turning on a sprinkler system without knowing it's condition can result in a nasty surprise water bill.
To say nothing about creating a quiet erosion problem you did not expect.
I am almost willing to guess that riser was not for a sprinkler but was providing some sort of remote hose bib so people didn't have to drag hoses around the yard? Was there only one valve and what did it look like? I wonder if it was the cut-off for that water supply line and not an irrigation valve. An irrigation valve in most places should have anti-syphon and anti-backflow properties for the safety of your home water supply and to meet code.
It would be weird to have an irrigation system with only one sprinkler unless you have a little postage stamp yard situation.
You do need to check things out before trusting an old system. Risers break all the time though so you may be able to tap what you have and build a nice drip system for shrubs and flowers. You will want to map out a turf system though. If it was a riser for a hose bib (I would have specified one to go into a below ground box) it should have had some rebar to support it.
Can you provide pics of the valve or valves and a description of how large the yard? And you might want to edit your profile to provide a basic location. That looks awfully shallow to me so hope you are in California or something where you do not have soil freezing problems.