Moles create shallow tunnels that would press back down in place just by walking on them ... not deep holes that you would fill. Are you sure these are moles? (We don't have a picture to evaluate.) There are other ground dwelling critters. A friend once had a mammal (I forget its kind but it wasn't a mole) digging up and destroying his back yard. He tried everything to get rid of them but nothing worked until he poured some gasoline, which has a lingering stink, in the holes.

Pouring gasoline into a hole in the ground is not only a really bad idea it causes pollution.

To get rid of moles you need to eliminate their food source- the grubs.

Treating for grubs is highly dependent on the time of year and their life cycle- you have to hit them when they are near the surface, Usually early spring- if you are in the USA I would contact my local cooperative extension agent for advice on specific timing in your county. Find them by googling "your state+county+cooperative extension."

Kanon- you don't give a location so it is difficult to speculate but holes with no dirt mound suggest chipmunks. Again- your cooperative extension agent is the best source of help with local issues. Or post a photo of the holes- that would help a lot. And location, of course.

Thanks for the replies.

I’m locates in SE Portland and I know it’s moles because they’re prevalent in the area, and because I’ve found a dead one in my yard.

Gasoline was never on the table, but thank you.

As for the reasoning behind my wanting to backfill the holes... In addition to the shallow feeding runways, I was under the impression moles also dig deeper, permanent tunnels and nests.

http://www.vegetablegardener.com/item/4311/much-ado-about-moles

Is that not accurate?

I’ll snap some photos this evening when I get in and post them up.

Moles in my hills is my nightmare too. Their tunnels route irrigation water away from my fruit trees and down the hill. Drip or slow stream widely distributed irrigation is a must in these areas.

They are relentless and so you must be even more so. ... spike traps and poison worms both work well for me. BUT if you have digging pets, delete the poison and double up on the spike traps. Its not unusual for me to have 4 or more set at all times. (BTW moles feed on grubs AND worms)

Always walk on your land with a pitchfork so that you'll be prepared when you see the ground getting bumped up. Just don't forget where your pipes are buried!!!