
I looked into what could be making these mounds. I didn't think we had many burrowing animals in our area and narrowed it down to the rather populous (at least in Seattle and the Pacific Northwest) Townsend Mole, aka Scapanus townsendii. The evidence left behind seemed to fit the crime. It could also have been a gopher, but they are relatively rare around Seattle. A Townsend mole, which is about 8 to 9 inches long and black in color, has a general population density where the typical city lot has one or two moles. Why we've never had them before is surprising although I've seen plenty of neighbor's lawns exhibiting some inhabitants.
According to Sunrise Pest Management, Townsend moles feed primarily on insect larvae, earthworms, slugs, centipedes, roots and seeds. We certainly have an abundance of those in our front lawn. When I was searching for solutions to our mole issues, I ran across a laundry list of things people do to try to deter them ranging from using poison, insecticides, smoke bombs or even burying razor blades. I don't want to kill-trap the mole and I certainly don't want to poison the little fella, even if he is making a mess of my yard. Any chemical agent or poison surely would affect the environment and wildlife from both land and sea, as the run-off from our yard goes directly out to Puget Sound and I can't imagine what mole bait and poison would do to the local fish populations.

Another option is a castor oil based treatment that I found on the Washington State Department of Fish and Wildlife website. I could save myself the money if the mole doesn't cease and desist and go with this completely non-toxic, cheap treatment instead:
Homemade Mole Control
Commercially available castor oil–based repellents have been scientifically tested on moles in the Eastern United States with some success. In theory, the repellent coats earthworms and other prey with castor oil. This renders the prey distasteful and, if eaten, gives the moles diarrhea. The moles supposedly then leave the treated area in search of a new food source.
The formula for the castor-oil repellent can be made by using a blender to combine 1/4 cup of unrefined castor oil (can be purchased at most pharmacies) and 2 tablespoons of a dishwashing liquid. Blend the two together, add 6 tablespoons water, and blend again. Combine the concentrated mixture with water at a rate of 2 tablespoons of solution to 1 gallon of water. Use a watering can or sprayer to liberally apply the solution to areas where moles are active. The above mixture will cover approximately 300 square feet.
The repellent will be most effective where it can be watered into the moist soil surrounding surface tunnels made by moles. Areas that receive extensive irrigation will quickly loose the repellent to leaching. For best results, spray the entire area needing protection; moles will burrow under a perimeter treatment.
The repellent may need to be reapplied before moles depart. Once moles move elsewhere, the solution usually remains effective for 30 to 60 days.
I'm not sure if I want to give my mole a bad case of the squirts, so I'll see if he decides to move on to someone else's property. But, if he continues as he has, he'll be leaving Le Château Duke on the Poop Express.
Photos courtesy of Sunrise Pest Management