We did 8+ day trips in Glacier and Yellowstone in back to back years a few seasons ago. Glacier was very strict. Lotteries. Specific tent sights. Not much flexibility in itineraries at all. There was a system for walk-ins, but as you noted you might be hanging on the porch and the chances of getting premium spots are likely low. Still, it is gorgeous country with dreamy backpacking trails.
Yellowstone was a last minute decision for us the following year because the trips we’d planned for 9 months were ALL on fire. It was a crazy summer where the entire Pacific Northwest was burning. We looked at a fire map of the west and Yellowstone seemed to be about the only place NOT burning. Drove through thick smoke from Seattle to Yellowstone, walked in to a ranger station and got our first choice, ideal trip itinerary in about 30 minutes. That included the mandatory bear video. This was over Labor Day weekend, too, when you’d expect it to be busy. Saw one group at a few hundred yards in the first 5 days. We were shocked. We asked the ranges why it was so easy get great spots in great places and they said it’s always like that. They estimated that close to 99% of Yellowstone visitors are within 100 yards of their vehicle at all times.
It was one of my favorite trips ever. Bears, wolves, bison – just about every critter you can think of. They behave differently in the backcountry than they do on the lawn at Mammoth for sure ;)
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