Case Western Reserve University may not be in the location he prefers, but it offers a B.S in Math and Physics degree–
http://physics.case.edu/undergraduate-programs/undergrad-degree-programs/bsdegree-mathphys/
Physics is another major that many math students consider.
CWRU also offers a Data Science and analytics Degree–
https://engineering.case.edu/eecs/academics/undergraduate-program/data-science-and-analytics
CWRU is nice because you apply to the school as a whole and so you can swap between business, Arts and Sciences and engineering up through junior year and mix and match majors.
Its a small, flexible research oriented undergrad program.
Carnegie Mellon offers some really interesting degree programs in their Dietrich school of Humanities and Social Sciences that are math oriented. I think their pure math degree is in the Mellon College of Science.
This statistics degree program includes machine learning!
http://www.stat.cmu.edu/undergraduate/majors
Purdue U in Indiana offers a fantastic Data Science degree too!
https://www.cs.purdue.edu/undergraduate/curriculum/data-science.html
I understand he might prefer U of Colorado, for location, and it is a very nice location.
but I would say CWRU, CMU and Purdue all will get him
a little stronger math education than the applied math program at U of Colorado Engineering, as applied math
is very small at CU Boulder, but growing.
Here is the applied math program at CU Boulder, its very flexible to double major–
https://www.colorado.edu/amath/
Note that he must apply and get accepted to CU Engineering to study applied math, as I understand it.
Pure math at CU Boulder is very strong as is physics, and those are in Arts and Sciences.
Physics is the single strongest department at CU Boulder, with aerospace engineering being good.
Applied math is very new and small at CU Boulder.
For applied math programs see New York University Courant Institute, Brown University and Princeton.
Those are top ranked programs compared to CU Boulder, but CU Boulder is trying hard to hire in top research scientists in the area of applied mathematics, if thats of interest.