I would like to fly from the Northeast to Seattle. Would someone be kind enough to point out the most popular routing to get through the Northern Rockies and Cascades. All my flying in that area has been at high altitude and looking at the MOA’s an the low charts looks like oxygen would be required. I know there are routes through the passes that do not require oxygen but do require good weather. I also have heard that there are named entry points and exit points on some of the routes through the passes. Any help would be appreciated.