Which mountain range was formed first (historically) and which the pedigree is correct?
If mountain range 1 was formed first, pedigree 1 is correct.

If mountain range 2 was formed first, none of the two pedigree seem correct.

If mountain range 1 was formed first you would first have the split of the initial population into population P and the population Q+R. Then, the formation of mountain range 2 split the population Q+R into Q and R. Therefore, Q and R are more closely related than they both are to P. Therefore Pedigree 1 is correct.

You can apply the same kind of reasoning by guessing that mountain range 2 was formed first and you will realize that you would expect a pedigree different than Pedigree 1 and Pedigree 2. If mountain range 2 appeared first then, the correct Pedigree would display the population/species/lineages P and Q more closely related to each other than they both are to R.