In the given passage, as per question, (S1) is the introduction. (Q) extends the information about Dhauladhar range started in the introduction. (S) is the next expansion of the information mentioned in (Q). (R) concludes a situation on the basis of the information given in (Q) and (S) hence, it follows (S). (P) extends the conclusion given in (R) and connects it further to a new situation. (S6) is the final conclusion, as per question, of the passage.