Looks like earth worm castings to me...

Yep, poor earthworms trying to function in spite of the barrier.

peeps pay money for such .. its a positive ..

and do get rid of the landscaping fabric ... its useless ... and actually a negative.. no matter what the marketeers say ...

moles sort of do the same .. but your scale is all off .. some moles are as big as your foot .. and other mouse sized.. but the hills are 6 to 12 inches across ... you could google images for that is you want ...

ken

Thank you so much, that's a relief. We've been plagued by many pests, furry and crawling. Glad that this is a positive invader. Last year there was an invasion of millipedes which destroyed all the zucchini. The landscape fabric is under the path between the rows of the raised beds.

"The landscape fabric is under the path between the rows of the raised beds."
As per Penn State " Some home
foundations have a border of river gravel or other mulching over a blanket of plastic sheeting or similar weed prevention barriers.
Millipedes will thrive under these conditions"
So, as Ken said, If you have an infestation, removed their breeding/living habitat in your garden areas..