muntdefems: Let's put it in some context...
phandom: Hmmm. You drew that?
It's a rather simple three-step process, really:
1. Sketch overarching area of cave. Add contour lines, but allow them to be thinly-defined. Make vague circles for openings like top or back of cave. Add smaller circles for rocks in foreground.
2. Begin to erase earlier sketch lines and fill in rock textures more. Fill in vague details, leave lighting for later. Use of a photo editing tool can be later used to alter drawing after scanning it in. If using a particularly sharp pencil, draw narrow crevasses and crags. Once satisfactory, move to the final step.
3. Give up, pitch out that garbage, and slap some Photoshop on some rocks.