i just a did a trip to Big Bear Lake, CA from Redlands, CA in a AP2 75D - left not fully charged at 160 miles (last minute getaway), started the climb up highway 38 with prob 145 miles and finished the summit and into big bear city with only 46 miles (18%)....interestingly the Tesla Navi is impressively accurate with range predictions.
Using 100+ miles of rated range doesn't seem all that surprising, as CA-38 is longer and tops out over 8300'. I'd definitely stick with CA-330 and CA-18 if range is a concern. Of course, during peak visitation periods, traffic is generally worse on the front of the mountain (330 and 18).
Came down a few hours later - Coming back down coasted down highway 18 (faster route) and made tightly with 8-9% to spare (which is what the car had predicted on it's navi). (shut A/C to OFF mode for extra margin).
Wow, you were brave to shut off A/C considering the heat we've been having. I don't care if our charge is going to drop to 3% or we have to slow down to make it - our A/C stays on if it's hot out!
Had you reached the base of the mountain in Highland, CA with insufficient charge to get home or reach a Supercharger, you could have plugged in at the evGo stations by Walmart. With a CHAdeMO adapter, this could be a pretty quick stop. Even without CHAdeMO, a bit of shopping (we like ALDI at the other end of the shopping center) would give you enough charging time.
Also big bear doesn't have any destination chargers or ideally a supercharger. The RV park was "closed" and a few Nema 14-50 sockets were out of order. This would be a good spot for one since it's a vacation/tourist/ski destination.
Totally agree about the need for more destination charging up here. One option, if staying overnight, might be to rent a cabin and plug in using whatever outlet may be available (might want to check with the owner as to available outlets). Otherwise, the best way to get destination charging is probably to ask for it whenever you can. Businesses will be motivated to install charging if they think this will draw more customers. Let them know that Tesla is willing to subsidize the charging hardware.
Also, while a Supercharger in Big Bear would be nice, I'm not convinced that this needs to be a priority for Tesla. They already have plans to put Superchargers in the San Bernardino Valley near the base of the mountain.