In terms of colleges that are currently hot for the undergraduate study of physics, look into Pomona and Hamilton. Pomona has produced two Apker Award recipients since 2018. Hamilton has produced two finalists within the same time period. The Apker, granted by the American Physical Society, is the nation’s highest recognition for undergraduate research in physics. As importantly, a Hamilton faculty member was recently recognized by the APS, receiving the award for significant research in physics combined with mentoring of undergraduates.
For another idea, research Wesleyan, which meets several of your indicated preferences.
I will throw out University of Texas at Austin, specifically the Turing program and Dean’s scholars there. UT Austin is generous with AP and dual enrollment credit, sometimes leaving only a couple of classes outside of math, CS and physics for a Turing major. The remaining requirements allow a wide selection of classes to meet. The university documents the path for in state tuition by the second year. It checks the boxes for warm climate. His application to Turing would be read by a professor, allowing his solo projects to stand out. Unfortunately the ‘stuff to do’ would be more city oriented, but Austin is a great city and the campus is a short walk/bike from the river.
First school I thought of was Washington & Lee. It meets mostl of the criteria (I didn’t hit warm weather although they’re all warm much of the year) - strong in physics/has CS, in the mountains and outdoorsy, you’ll know your profs. Less strong but similar would be Sewanee - both of these are in small mountain towns. Out West, Reed might fit the bill - near the city but near nature.
Two others a tad bigger - Colorado School of Mines (it’s Engineering Physics) and South Dakota School of Mines - smaller schools, like W&L, nature abounds - maybe less on the partying but there’s partying everywhere. Davidson - has trails, etc. nearbound but I wouldn’t call it in nature.
You can throw in U of Denver and Montana State too and maybe UVM and to get a little crazy as it’s much lower ranked/known but U of Maine.
He can get a great education anywhere - but these schools I think fit the bill.
The internship part - some of that is top schools but mostly it’s going to be him networking, applying - and he should find the right fit. There’s no guarantees - even if you go to Harvard - but in my mind, this is a good set of schools - but not sure of geography other than outdoorsy and small classes, etc.
“The LeRoy Apker Award recognizes outstanding achievements in physics by undergraduate students, and provides encouragement to students who have demonstrated great potential for future scientific accomplishment. Two awards are presented each year, one to a student from a Ph.D. granting institution, and one to a student from a non-Ph.D. granting institution.” LeRoy Apker Award (aps.org)
The 2013 recipient from a Ph.D granting institution was a Wesleyan student: Prize Recipient (aps.org)