Altitude camping
A lot of the best free camping on public land is high — national-forest country in the Rockies and the Sierra sits you up where the air is thin, dry, and cold at night even in summer. The autonomy card on this site reacts to that height in exactly one way, and it's easy to read more into it than it means: when your pin sits up around 8,000 feet or higher, and only if your rig carries a furnace, the card assumes the nights turn cold and starts burning your propane faster. That's the whole of what altitude does to the math. It won't add water for the thin, drying air, it doesn't know a thing about your body, and if you camp without a furnace it doesn't react to how high you are at all. Here's the plain version of camping up high: the one thing the card changes, the danger that the mountain hides in your own head, the weather that builds fast, and what the climb does to your rig.
The card changes exactly one thing for altitude — and you still own the water
The one place your elevation touches the card is propane. When your camp's pin is up around 8,000 feet or higher and your rig has a furnace, the card figures the nights will be cold, so it burns your propane down faster and tells you why right on the page — something like "expect cold nights, your furnace runs, which burns propane faster." That's it. If you're parked lower than that, or you don't carry a furnace, the card doesn't react to your elevation at all — it runs the same tank math it would at sea level. And here's the part it can't do for you: thin mountain air is bone-dry and you breathe harder up high, so you lose water faster than you would down low — but the card counts water at the usage number you set and never raises it for altitude, the same way it never raises it for desert heat. Before a high trip, go into the rig profile and raise your per-person water usage so the days-of-water figure is honest for where you're going. I won't hand you a gallons-a-day number; it depends on you and how hard you're working up there. Set it high, watch your tank.
Altitude sickness is real, and the fix is down
Go up fast and sleep high and the altitude itself can make you sick, fit or not — I'm a camper, not a doctor, so learn this properly from a real source before a high trip. The mild version is a headache, no appetite, feeling queasy and wrung out, and not sleeping well the first night up. That usually eases if you stop climbing and give your body a day to catch up. But if it's getting worse instead of better — a headache that won't quit, throwing up, staggering like you're drunk, confusion, breathless just sitting still, or a wet-sounding cough — that's the dangerous version, and the real fix isn't a pill or toughing it out, it's losing elevation: get lower and get help. You lower the odds by climbing gradually, sleeping lower than the highest you got that day when you can, drinking plenty of water, and taking the first day up easy instead of hammering a big hike. Know the difference between "I feel rough" and "I'm getting worse," because up high the second one is the one that matters.
The weather builds fast up high — get below the trees
Mountains make their own weather, and they make it in a hurry. Afternoon thunderstorms stack up over high country fast, and above treeline you're the tallest thing on the ridge — lightning is a real, get-off-the-high-ground hazard, not a someday thing. The old rule holds: climb early, and be heading down off the exposed stuff by early afternoon, when storms usually build. Wind, cold, and hail come riding with them. The weather strip on a camp page can flag that a system's in the area, but it's a broad area forecast — a valley pin and a pass two thousand feet above it read almost the same on it while feeling nothing alike — so use it to know a system's around, then watch the actual sky and the sky upwind. If it's already turning hot-and-dry or cold, the hot-weather and cold-weather notes carry the rest.
It freezes up high, even in summer
The higher you sleep, the colder the night, and high country can drop below freezing on a clear summer night without much warning — that's the exact reason the card burns your propane faster up there if you run a furnace. Don't pack for the warm afternoon and get caught shivering before dawn: bring the layers and the sleep system the cold-weather note walks through, even on a July trip. In the shoulder seasons a cold night at elevation can freeze a water line, a hose, or a wet filter overnight, so keep water where it won't turn to ice. A warm day and a hard-frozen dawn aren't a contradiction up high; they're the same twenty-four hours.
The sun is fierce, the air is dry, and it's tinder up there
There's less atmosphere overhead to soften the sun, so it burns harder up high — you can cook your skin and your eyes on a cold day at altitude and never feel warned by the temperature. Cover up, wear real sunglasses, and mind the glare off snow if there's any left. That same dry air chaps you and quietly pulls water out of you without making you feel thirsty, which loops straight back to setting your usage honestly. And dry high country in late summer is often tinder — a lot of forest sits under fire restrictions or a full ban when it's hottest and driest. Don't guess either way: check the unit before you strike a match, the way the fire-restrictions note shows you how.
What the climb does to the rig — and none of it's on the card
Thin air costs the engine power. A loaded rig that pulls a grade fine down low can crawl and strain up high, so don't be surprised by it — give yourself room, keep an eye on the temperature gauge, and don't flog a hot engine up the last pitch. Food and water cook slower up high, too, because water boils at a lower temperature the higher you get, so meals and boiling water for coffee or cleanup take longer and lean harder on your propane. The card counts your propane, but it doesn't know your stove is working harder up here, so it drains a little faster than the number on the page — the same kind of blind spot as the water. Your food days aren't really the worry there; but you're working harder up high, so carry a little extra margin anyway. And on the way down, a long descent will cook your brakes if you ride the pedal: gear down and let the engine hold you back instead. None of this shows up on the card; it's rig-and-road reality you carry yourself.
One honest split to end on, same as the hot and cold pages: the tools here help, but they don't feel the mountain for you. The autonomy card is tank math, and for altitude it changes exactly one thing — propane, and only if you run a furnace — so it's honest for a high camp only if you've raised your own water usage and you know your stove is leaning harder on your propane up there. The weather strip on a camp page can flag a system moving through, but it's a broad area forecast, not the temperature or the storm risk at your exact elevation. And the map draws water and services in a straight line, which in the mountains can mean a long, switchbacked climb or descent to the nearest tap you can trust. So raise your usage, climb slow, and get below the trees before the afternoon.