I'd check on the outing clubs at the schools on your list. I notice, looking at the directory of the Intercollegiate Outing Club Association that this group has expanded beyond its original geographic location in the northeastern US (I even found Oregon State University there!). These clubs give you plenty of opportunity to carpool to more distant locations. You don't need to be limited by a bike.

I spent one year at Cornell University eons ago. There were Outing Club trips every weekend, ranging from dayhikes to local waterfalls (the countryside is almost as beautiful as the Columbia River Gorge out here) to weekend trips to the Catskills and Adirondacks, all over New England and a week-long ski trip to Mont Tremblant during January's semester break.

I do want to reiterate that as a grad student, you're not going to have very much time for this sort of activity! You'll necessarily be spending all your "school vacation" time doing your thesis research!