It turns out Zone 9 of our irrigation system was not working. It took a while for us to notice, since the system runs in the middle of the night, so we did not see it not watering. It may have been intermittent since in one case, it came on after leaving Zone 9 on at the controller for about an hour. So I figured it was probably the valve.
First problem is finding the valve. I eventually found it, after some trial digging, and looking at the old photos from when the area near the gas meter was dug up years ago.
I contacted American Irrigation Repair, since they had done good work on previous irrigation system repairs that are over my head, and they came out after about 2 weeks.
They agreed that it was the valve -- the wiring is okay, but the value didn't work, so they replaced it. $223.61.
I took advantage of the need to replace the valve, to redo some of the plumbing. There are two heads for Zone 9 that are for the front lawn. All the others are for beds in the West Side and around to the back. So instead of the previous T connection, they put in a 90 degree turn to go to the back of the house, only.
The next day, I trenched from the nearest head on Zone 10 -- for the front bed, near the corner of the house, over to one of the two heads for the front lawn, and connected them.
Then I capped off the part of the pipe near the Zone 9 valve, and now the two front lawn heads are on Zone 10, which covers this entire side of the front lawn. Zone 11 does the other side, between the driveway and the sidewalk.