We can speculate that consciousness is some kind of a representational process, using non-verbal, non symbolic representations. We can suppose that what is being represented is in part the state of my own body, and my current interactions with the external world. So this is not a static type of representation, it is a continuously changing representation, which is representing a real time 'dance' between my body and the world. So, returning to your (excellent) analogy of the field of rocks, the field of rocks would not be conscious unless and until it becomes an emergent representation of itself and its boundary with the rest of the world, all happening automatically and in real time. The field of rocks has no sensation of the sun's warmth because it has no representation of warmth, and no way of moving or changing it's own body as a response to that representation of warmth, and no attentional mechanism to prioritise how it responds to representations of warmth, hunger, thirst etc.
Once you start to think of consciousness as a representational process you start to see how consciousness might become an emergent phenomenon inside a machine 'designed' for creating representations. A machine like a living animal.
Of course, that puts you in the position of having to explain what is a non-symbolic, or non verbal, type of representation. But that's doable, I think.