Once more I'm in the world of British comics from the 1960's/1970's... Hotspur, Rover, Beezer, Topper, Victor etc.
This was one that went on for a few months.
A small town (maybe in Wales but I'm not sure) has a mountain range nearby, including one that's slightly darker than the others. Geologists or miners start digging at a side of it one day and then all stand back in awe. A few hundred yards away some sections of rock crumble away and a large eye is glaring out at them.
There are shenanigans for a while as scientists are helicoptered in but by the time they arrive the beastie is slowly moving, I think towards the town. Herds of farm animals disappear but I can't remember how it moves fast enough to catch them.
The army rigs up a defensive live and use mortars to try and stop it but it keeps moving. I think it can do like an extending mouth (Alien Xenomorph!) and gets some soldiers yum yum.