I see several dirt mounds in my backyard. These are usually around 6 inches in diameter with no obvious hole caused by an animal. Can you please help me identify what is causing it and also how to stop it?
I am from the Seattle area as well. I've done most of my career in the PNW as a Landscape Architect. Part of my career involved landscape maintenance just to have a job. Ran 7 crews and I was there hands on for 4 years as foreman/supervisor.
Moles and gophers and sometimes voles become part of the landscape's soil. They are a GOOD thing. They do not overpopulate. Rarely are there but two of moles or one of gopher. Yours looks like a gopher. Larger hole and running around your landscape instead of your lawn.
These animals eat insects, grubs, not plants normally. If they are there they are eating grubs or larvae that could cause a problem if you kill these animals. When you run out of grubs/insects they leave to go to the neighbors.
I once thought of 'rent a mole' where I would take a few sweet little moles and allow them to reduce populations of crane fly larva, aerate and top dress and charge people money for this service. If I ever caught a 'wack a mole' person I would probably bury them in the compost heap.
Just sweep the piles of soil off your hardscape. Relax. You've got some free service little guys that are wonderful. And I am not charging you money. These guys aerate the soil. They recycle the soil. I charged big bucks to 'top dress' lawns and beds. These guys are doing it for free with your own soil while at the same time providing aeration. And keeping the damaging (crane fly larva in your area) in control!
Piles on your lawn or beds or patio? Take a rake and simply flip that soil onto the top of your lawn and beds. There is a reason for the subsurface preparation of hardscapes and this is a good example. They aren't able to come up with the rest of your patio, just these informally laid blocks.
If you live in Seattle, I gotta tell you you have access the the BEST mulch for ornamental beds and lawns in the world! Call Sawdust Supply and ask about Gro-Co. You are so dang lucky! I was able to tell clients to find another company if they wanted to use bark for mulch. Ugly and oh so worthless for the soil.
This Gro-Co mulch is flat out amazing. More beautiful than any mulch. Feeds the soil organisms. Put this on your beds and your plants will blow you away within one week. It is human poo plus sawdust COMPLETELY decomposed. Perfect texture, dark taupe, no sticks or stones and the best thing is no weed seeds no pesticide residues! There are mulches and composts added to top soil that one can't grow a petunia because of the pesticide residues.
You are so lucky and if you want to know more, ask away.
Those mammals in your soil are a benefit! Do you have a compost pile? That attracts these animals so if you do want to eliminate them get your compost further away from your home or put it in a composter barrel. Above ground. The soil beneath the compost will be very active with grubs/insects.