Williams outing club is very active and well resourced, also science majors seem very happy and geology department is outstanding. Lots of outdoor leadership opportunities (leading orientation programs, JAs, etc.)
I coach on our HS mountain bike team and we’ve sent several students to Ft Lewis College and Colorado Mesa University. Both have very strong MTB programs, and off season there’s road riding (cleared roads) and of course snow sports. I know less about their STEM programs.
I’m also in CA and, honestly, almost anywhere in CA has good mountain biking! Occidental and Caltech (unparalleled STEM) in Pasadena have easy access to the San Gabriels; UC Davis isn’t far from Downieville trails; UCSB has the Los Padres NF, etc…
You might look at Oregon: Reed College has a pretty outstanding STEM program (esp. in physics) and easy access to trails in and around Portland. I haven’t ridden near Oregon State/ U of Oregon but seems there’s great riding everywhere in Oregon and never too cold (always too wet but hey).
Wow— so much great info here. Thank you all so much!