He knew that the ledges had not been touched, that no artifice had altered the unplanned beauty of the graded steps. But she seems to think that this natural beauty is only a stepping-stone to the greater beauty of human creation, which gives meaning to nature. Rand was deeply interested in meaning, and I think it is for this reason that she held aesthetics to deal mainly or even exclusively with art rather than aesthetic phenomena in nature. The connection here to the idealist tradition of 19th century philosophical thought on art is not hard to trace.
Art instantiates a conceptual body in perceptual raiment.
Thus nature can be beautiful, but for Rand nature carries no meaning of the kind art can. That essence, as the essence of all meaning in human life, is conceptual. At least, this is how I read Rand on art and aesthetics.