Are some of you confusing gophers for moles?
With moles you can see the whole tunnel system as an upraised route, they don't make mounds like gophers.
Moles only eat insects and won't damage your plants or lawn, gophers will. If you have a lot of them they're there because you have insect infestation. Like KennyM said get rid of the insects and the moles will leave. Otherwise just leave them alone, they're a beneficial animal.
Since moles feed heavily on grubworms, the elimination of the grubs will decrease mole activity in a lawn. Grubworms can be controlled either with chemicals or with milky spore disease, a relatively harmless biological control agent. Chemicals that may be used by the homeowner include: Diazinon, Dylox or Proxol, Oftanol, and Sevin (Carbaryl). After treatment with any of these insecticides, soak the lawn surface thoroughly.