If you have ADS-B out or TABS, the FAA has a record of your airspace compliance (both barometric and GPS altitudes).

https://www.faa.gov/nextgen/programs/adsb/faq/#g7

ATC's network of ADS-B receivers provides coverage in many places where radar is blocked by mountains. ADS-B Performance reports are eye-opening wrt coverage https://adsbperformance.faa.gov/paprrequest.aspx