I would charge to 100%. That is a lot of elevation to gain from Sandy to Timberline Lodge. Here is my trip report from 1/22/12 on the other side of Mt. Hood. I was driving the LEAF to both Mt. Hood Meadows parking lots this winter & always arrived with 2-4 bars and only used 1-2 bars coming home. I have been working with the sustainability director to try to get them to install L2 there. Have a great trip to Timberline, let us know how it goes.
1/22/12. Mt. Hood, Oregon hill climb today, 3736' up. I did 100% charge with preheat ending with to 1.5-2 bars left (19 on the GOM) from 30-24 degree temperatures, all on snow, total miles was 52.2. I started in Odell, OR, 725' elevation and went up to Teacup Lake Nordic ski area to cross country ski, 4461'. I drove between 35-50 mph going up and got there with four bars remaining and 13 miles on the GOM. I have 17 lb. wheels, with General Altimax Artic, siped and studded tires filled to recommended psi. I coasted back down the mountain, reaching up to 53 mph at times, but mainly was going about 40-45 mph. I used my heated seats, and only used the defrost at 60 degrees when the windshield needed it, both ways. Fun experiment. We have had snow and ice since last Wednesday and this car performs very well with the low center of gravity, traction motor, and studs. I could not be happier with the handling of the LEAF in this winter weather.
. Good location with Easy I84 freeway access. I did not see any L2 
