Getting in mountain shape with no mountains around?

Before U.S. Fish & Wildlife killed off the trout in the Grand Canyon, we backpacked for a week every year. The climb out is mentally daunting for first timers. One step at a time, is what I told them. My dad did it at 67, and he wasn't in great shape.

One year I hiked out with a couple of women who had Camelbacks. I was still using bottles. They drank more water because it was convenient. After I bought a 70 oz. Platypus bottle with tube, I found the hike out much easier.

My friend drinks around 140 oz. (almost 9 lbs.) while hiking and hunting. I find 70 oz. enough if it is cold, but for an October hunt I take an extra pint bottle. Don't forget that NM is much drier than you're used to. People get dehydrated with just mild exercise.
I used to bring a rod down every time I backpacked the backcountry trails - trout fishing was amazing! But don't blame US Fish and Wildlife - it was primarily the GCNP and the NFEC program.

I could care less about the humpback chub - bring back the trout! White people aren't native to the GC either, so why not give it back to the Indians?
Having been on high mountain hunts I will give you this as best advice. Train a lot running bleachers, stairs, and other structures with a back pack. The next is go in as far in advance as you can and get acclimatized to the thinner air. My first alpine hunt, I was 32 years old, in the military, and had been running up the side of a 600 foot rise in elevation with back pack. My guide was a 63 year old man and when the hunt started he walked my *** into the ground leaving me huffing and puffing at just over an hour of the hike. Try shooting a 300 yr shot on a chamois with your heart beating out of your chest and trying to slow your breather. Fun challenge. Knowing I was going again in another country for Ibex, I trained for a year. My buddy who was a Queens gaurd for the Queen of Holland joined me for a 2 on 1 guided hunt. He shot an Ibex at above the treeline and we had a 4 hour walk down. I offered to carry half the animal or switch off with him but his pride only let me carry his gun. When we got to the parking area where we started he fell over, almost had a heart attack, and we almost had to take him to the hospital. Rule of thought on that is don't turn down help, being in great shape helps but when you live at sea level the thin mountain air is brutal and don't let your pride kill you. The lack of O2 is a huge factor another buddy to sent to Bolivia. As a runner he when out first thing next morning and started running, short of it was he died of a heart attack less than 20 minutes into his run.