Seconding the Claremont Colleges. My daughter isn’t vegan but a number of her friends are, and they eat very well. Fresh fruits and veggies abound. There are actually seven dining halls on the five campuses, all walkable and all with good vegetarian and vegan options. There is an app, developed by a Harvey Mudd student, that displays all of the menus so that students can decide where to eat. Search “Claremont Menu” in your app store and you will find it. 
Have you found this tool already? https://www.peta2.com/feature/vegan-college-ranking/
The Claremonts get a 100% rating. So does Colorado College, which came to mind when you mentioned access to outdoor recreation.