Although the outcasts are actually heading towards Sandy Bar, due to the tiredness of the travellers, and in particular the reluctance of the Duchess to go any further, the group stop and make camp at a place on the road. This location is what I assume you are referring to in your question. The description of this location appears to be particularly inviting. Note how the narrator describes it:
The spot was singularly wild and impressive. A wooded amphitheatre, surrounded on three sides by precipitous cliffs of naken granite, sloped gently toward the crest of another precipice that overlooked the valley. It was, undoubtedly, the most suitable spot for a camp, had camping been advisable.
Thus the travellers find a spot that is ideal for making camp, and thanks to the tiredness of the Duchess, and especially the alcohol that they all consume afterwards, the travellers lose all desire to carry on further up the narrow and precipitous track, and thus they all stay there.