That sounds like a 1 tank trip if you are just cruising along.
If you're riding hard I'd say over 60 but easy ride up to 100. A 70mile loop on Jeep trails should be just fine. Maybe like hondasxs mentioned bring a little extra but shouldn't need. If you feel it miss at all just shut it down right then and add fuel as long as you don't totally run it out it'll fire back pretty quickly I would believe. Don't plan on that many in reserve but if r's are kept steady at medium speed and you are easy on hills it'll do it
I do the utah skyline loops all the time at elevations 8k to 10.5k exactly as you described and usually travel 125 mile round trip on 5 gallons. i have never hit the last bar yet. jeep trails and dirt roads 20-40 mph mostly . other threads have shown mpg listed . i average 23-27 mpg all the time. i also use Lucas fuel additive.
We've always carried a manual transfer pump in case of someone running out. With kids and dirt bikes (even with a reserve,dang kids
) someone's always running out. To date we have been fortunate enough not to run out
i love the mid panel, it cuts down the dust. not as good with my windshield but when i use my half windshield it catches the wind and forces it on to the engine and pushes the heat out the bottom between front seat and bed. no heat issues when i use the mid panel and the 1/2 windshield. winter is best for windshield as the heat stays in bur does add more dust .
this is what i use in all my machines and it work very well. add a few oz per tank and also use 91 octane fuel you will see better fuel mpg . 
