It's not rare at all. If the black forest you are in is small and doesn't have much copper, rest assured that there are a whole lot more black forests out there. If you only have one node close to your base, go ahead and dig it out. Those things are huge. You will end up with a massive crater. If you have several nodes close by, then just taking the tops off will be faster because you won't be digging up all the dirt at the same time.