Flatrock, the little town of about 1,500, where I live in Newfoundland, is home to some unique rock formations and geology going back a million years or more. The smooth flat rocks stretch out from the land into the sea and were supposedly used for drying cod many years ago. Other rocks are like stacks of huge square boulders lying on their sides, one on top of the other. I'm not a geology expert but love looking at the rocks and their coverings of lichen, additional boulders that the ocean has deposited onto rock shelves and, of course, the gulls' antics around the rocks and water.
Drawing rocks is no different than any other subject and if there are a lot of them I break the scene down into sections to make it easier to deal with. Drawing intricate scenes can be perceived as difficult, but in reality it isn't. It's time consuming and realizing that, I make a commitment of slowing down and studying a scene carefully which makes the drawing a lot easier than rushing and ending up with a poor sketch.
I did a pencil sketch on site which took about 30 minutes, then took the piece home to finish it in the studio. I added ink over the pencil, then coloured pencil. Colour notes in the sketch book for rocks and ocean along with the photo to enhance my memory provided the colour cues I needed. And if I am stuck I can just wander down the road and have another look in real life.