Many are easy to spot if you know what to look for.

If you do a lot of terraforming, then you should be familiar with how steep a slope can get.

When the game creates the mountain cave on a mountain side, the game creates an almost vertical slope on the mountain that is unobtainable from terraforming. So I just run around looking for these vertical slopes and there is always something there, usually a cave, but sometimes it can be other things like an egg.