Not entirely sure I agree with the other posters on this one. While it is fait to say that squatting is the king of all leg exercises when i think about your goals which I'm guessing is a general fitness increase as opposed to bulking up.
Now I in no way think that a couple of sets of heavy squats twice a week is going to hinder you in your aims I'm not sure it's vital.
If you consider the exercises that you will be doing while out hiking and climbing particularly if performed with a heavy rucksack you will be subjecting yourself to a fairly strenuous workout. I think it would probably come under the term of GPP which is I believe a conditioning regime which emphasises real life functional movements which condition the body superbly.
Other examples of GPP would be; sled-dragging, shovelling snow, splitting wood, loading and unloading weights etc etc. Now admittedly not all of those are practical for everyone, particularly in this country, but still, I hope you get the general idea. If you challenge yourself while your out there you'll be using muscles you never knew you had and i'd imagine you'd be pretty pleased with the gains in fitness you made.
Just my opinion of course.