I was not a big fan of Notre Dame before my daughter went there but my view has changed over time. Boulder is a wonderful town while South Bend is a working class, midwestern medium sized city. You can't totally ignore the surrounding area when picking a college but remember that 95% of your time will be on campus
In terms of academics the admitted student 50th percentile ACT range for CU Boulder is 26 - 32 on the ACT while the same 50th percentile for Notre Dame is 33 - 35. I'm not sure that I would agree with someone saying that they are equivalent academically. Notre Dame has about 8,000 undergraduate students while CU Boulder has 31,000. There are two other data points you might want to look at - Google each schools Common Datasets - these would be (a) the percentage of students completing the full 4 years in four years or five, and (b) the profile showing average class size. If you do well in large class settings this may not be important but it is one major difference between a more selective/wealthier school and a large flagship public university. 46% of CU Boulder's students finish in 4 years, while Notre Dame has a 93% graduation rate.
An older report detailing distance and middle distance women's program
http://www.ustfccca.org/assets/symposiums/2013/Connelly%20-Notre%20Dame%20Cross%20Country.pdf
A workout wed. video from Flotrack
https://www.youtube.com/watch?v=vhL0P1vndgI