Probably in your digging you may have collapsed it and its further away from mound. He won't bother coming to that mound again as it is definately air tight.
Take a long screwdriver and poke around you should be able to find a tunnel. You can place the black box type at any tunnel and its lights out for him when he attempts to make it air tight.
Or you can always flood the area and then poke around. When water runs quickly to area you've found one...maybe.
Then wait for him to dig again and act quickly.
I have flooded them before and usually they just move 6-8 feet away.

I have to dig a pretty big hole to find the tunnels, and they are often deeper than I expect. The hole I dug into the lawn was about 20 inches in diameter and went down about nine or ten inches. I found two tunnel holes at about six inches and a big tunnel at about nine inches. I also use the hose to find them.
Renee

The main tunnel may not be directly under the center of the mound. The feeder tunnel may start at the edge of the mound and is most likely back filled with dirt.

You can get a general idea where the main tunnel is by the placement of the mounds.

Dig down around the perimeter of a new mound. Dig down about a foot..sometimes more and sometimes less depending on the soil conditions and the age of the gopher. When you have a large hole use a screw driver to probe the edges of the hole. When you find the soft spot follow it with a shovel until you find the main run.

If you have underground sprinkler lines look there first as they like easy digging.

Zeuspaul

I made a 'probe' from a sprinkler tool - basically it's a long metal rod with a "t" shape handle which is used to turn on/off valves in the ground. The curved part on the end needs to be cut off... This probe is almost 2 feet long so it can be used to find deeper tunnels. When you have a mound, explore the area in a circle at least 1 foot around the mound. Push the probe straight down and feel for when it hits an air pocket - it will go down suddenly for a couple inches when you probe into the tunnel. Probe every few inches in the circle around the mound.

When you locate the tunnel dig a small hole to expose it - smaller is better since it will need to be covered later.

If you can I like to "follow" the tunnel as far as I can before setting a trap. Often the tunnel will lead to a larger main tunnel.

Traps in each tunnel opening can be 'baited' with grass etc. - not a lot, the opening should then be covered ( a big stone etc. I have some leftover slates which are perfect)

The black hole is a tricky trap to use, it must be placed exactly inline to the tunnel and have the opening fit perfectly to the hole. Any light here will warn the gopher. I used to make a vertical cut on the tunnel opening before setting these traps. Cover the entire trap with loose dirt - only leave the back uncovered. At times I baited my black hole with a piece of carrot.
I much prefer the Macabee style traps...

Well thanks for your feedback everyone .

I probed around with a garden stake and found a tunnel, so I put a trap in and we'll see tomorrow morning if it works. I don't think it will work, since I only have one trap and didn't know which direction to place it and if that was the freshest.

I am holding off buying more traps trying to figure out which brand is easiest to use. (Right now I have the Black Box by Victor.)

While I happened to be digging up some Picea Glauca conicas, I inadvertantly discovered a tunnel as well.
Can there be gophers present without any visible mounds near by?

If you put the black box at the end of a tunnel near the mound with the open end at the tunnel you don't have to worry about which way.
He will just try to plug it and then its lights out for him. I dig out the mound and set it there all air tight.
That is how I use it but make sure you cover all the little holes, edges, sides and bottom air tight or he will just plug the beginning of it and not get caught.

I like the Victor black box best. The black hole traps fall apart after a couple of years.

I have had good luck setting them at the end of the hole as indicated by gobluedjm or in the main tunnel.

If you set one in a main tunnel just keep at it until you get it. Just leave the other half of the tunnel open. You will soon find out which side he is in.

The tunnels sometimes go for ten feet or more without a mound.

You usually catch them in a day or two. I have caught a few after leaving the trap for a week while I await for new signs of where he is.

Zeuspaul

Well the trap has gone off two nights in a row, and no dead gopher yet. The tunnel was plugged up the second time, do I keep the trap there in the same hole? What am I missing? Does it have to be really flush to the hole, mine was pretty level but not perfect. Thanks, if anyone has any insight!

He plugged it cuz he detected air. He will plugg the first air spot he detects. The trap has to be air tight and covered well around the bottom, tunnel opening and all the holes of the trap metal parts. If you have the trap air tight most of it will be covered with soil especially at the tunnel opening. Pack soil tight around it.
You have to have the trap air tight except the opening at the end, when he attempts to plug that..its lights out.
It took me twice to figure that out and then I got him once it was air tight. So yeah you can keep in same hole unless he's really smart ;)

I have better luck if I slide the trap as far down the tunnel as my arm will reach. I lay on the ground and use a screwdriver or a dowel to push it waaay in there.

Any tunnels you find should be set with traps. If you buy the green jaw-type traps at Lowe's for 12 bucks you get two. That's what I used to catch my gopher. If you use that kind of trap, you just leave the tunnel open to the air, and when he comes to investigate the air flow and to plug the tunnel he trips the trap.

You can set the jaw-type during the day as well. My gopher tripped the trap the night I set it, I reset it in the morning, and an hour later I had him.

I am currently battling the Big Bad Daddy Gopher in the back bed. He has sprung the trap twice, but I'll never surrender my territory, even if I have to do like the Russians and burn every village all the way to Moscow.

May the garden gods be with you, elvie.

Well I thank you guys and the garden gods! First one is caught, I feel encouraged and , and have two traps set in other tunnels.

If you live in the northern third of the state (or in Oregon), the Black Box/Black Hole types may be too small for the subspecies of western pocket gopher that you'll be going after. The best trap in that case is the Cinch Trap, which is the one used by the U.S. Forest Service. You can often find them on Ebay.