You you cannot direcly dig those two ridges under arrows. To solve this you need to add soil to the two nodes under arrows (behind the ridges) so the ridge disappears on one side and you can dig it from the top. And you should be careful digging from the center because the slope may block you from raising terrain under arrows.
You can see that all the surrunding area are filled with dirt,i cant place more dirt to get off the ridges, and i cant dig between them, because of the big difference of hight. Seems to me an unresolvable problem:D
I'd advise you to first work on the middle part (blue-ish) until you can raise the surroundings and only then you'll be able to get rid of the marked ridges. It'll be really tedious, though
After looking at it for a while, I'd also say that it is not removable, but Marp might be willing and able to help you out, if it is that important to you. You might not even need to wait until next xmas for it, who knows. ^^
Need something? Here is my Shop (Including some useful info for new/returning players at the bottom of the first post)